Information
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Site conducted
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Document No.
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Area or Zone being assessed
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Site
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Conducted on
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Prepared by
Assessment
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Assessment to comply with the Dangerous Substances and Explosive Atmospheres Regulations 2002
Dangerous substances can put peoples' safety at risk from fire and explosion. DSEAR puts duties on employers and the self-employed to protect people from risks to their safety from fires, explosions and similar events in the workplace, this includes members of the public who might be put at risk by work activity.
Dangerous substances are any substances used all present at work could, if not properly controlled, cause harm to people as a result of a fire or explosion. They could be found in nearly workplaces and include such things as solvents, paints, varnishes, flammable gases, such as liquid petroleum gas (LPG), dusts from machining and sanding operations and dust from foodstuffs.
The need to produce a DSEAR risk assessment is determined by the definitions shown in Section 1. If a dangerous substance or an explosive atmosphere does not exist, the regulations do not apply and no assessment is required -
Substance Name:
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Category (select all that apply)
- Explosive
- Oxidising
- Extremely Flammable
- Highly Flammable
- Flammable
- Explosive Atmosphere
Data sheet information (see also Section 1)
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Flash point
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Auto ignition temperature
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Lower explosive limit
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Other
Useage
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Where used/generated?
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Amount used/generated (specify units of measurement)?
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Amount stored (if applicable) - specify units
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How stored?
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Can substance be eliminated/substituted?
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Specify replacement
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Measures currently in place (describe/photograph)
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Photograph
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List potential ignition source(s)
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Examples could be an electrical spark caused by connection or disconnection of leads to a battery, naked flame eg pilot lights, smoking etc
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Employees at risk
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Relevant operator and/or supervisor training
Assess the risk
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In order to assess the risk select the appropriate items below related to this assessment (see appropriate guidance section as appropriate)
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Rating:
Severity
1 - Small localised fire easily extinguished or contained in plant explosion causing no damage. No RIDDOR reporting required.
2 - Explosion or fire causing plant damage and requiring RIDDOR reporting.
3 - Major fire or plant wrecking explosion with significant injury potential.
Probability
1 - Good process control and unlikely to occur except in unforeseen circumstances.
2 - Events likely to occur if there is an established systems failure.
3 - Process inherently hazardous or controls in place simply not good enough.
Bulk storage of flammable liquids (Select yes to see guidance)
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Bulk storage of flammable liquids?
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BULK STORAGE OF FLAMMABLE LIQUIDS
The information below applies to bulk storage of flammable liquids with a flashpoint of 55ºC or below. The precautions would also apply to liquids with a flashpoint above 55ºC where for process reasons or purely viscosity reasons that liquid is heated in storage to above its flashpoint.
Tanks should be designed and constructed to appropriate standards which may include:
BS2594 Carbon steel welded horizontal cylindrical storage tanks.
BS2654 Vertical butt welded shell tanks for the petroleum industry.
BS4994 Tanks in reinforced plastic.
Sources of ignition must be controlled (See D.11). The obvious one is that of electrics and there is a DSEAR duty to zone. Zone 0 will be inside the tank. Zone 1 will be around the vent and Zone 2 will be within 3 metres of the tank in any direction. (See D.15).
As regards distances, as a good rule of thumb the tank should be 6 metres from any boundary and from any other building or process. If there is more than one tank there should be 2 metres between each.
If there is an LPG tank in the area then the distance between a fuel tank bund and the LPG tank should be 3 metres but if the flammable liquid stored is highly flammable this distance should be extended to 6 metres.
As regards delivery tankers, the connection point should preferably be outside the bund to cut down the length of hose attachment and there should be firm horizontal standing for the tanker. This filling point should be 10 metres from any buildings or boundaries. The connection point should have its own small bund.
The tank should be fitted with a bund wall capable of taking the contents of the largest tank together with a further 10% to allow for a foam covering in case of leakage. The wall of the bund preferably should not exceed 1.5metres in height and should be capable of taking the hydrostatic pressure.
The floor of the impervious bund structure should have a slope of 1 to 50 to one end where there should be a sump for the collection of rainwater which should be pumped out. Preferably there should be no valve connection to the outside.
Underground tanks are permissible. There is obviously a reduced fire risk but there are problems of maintenance and leak detection. The distance between an underground tank and a building with a basement should be at least 6 metres. It is probably that the tank will have to double skinned as well as having a leak detection system.
Further information relating to this topic and the handling of flammable liquids may be found in HSG176 entitled “The Storage of Flammable Liquids in Tanks” ISBN 0 7176 1470 0. -
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Flammable liquid storage in containers (select yes to see guidance)
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Flammable liquid storage in containers?
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FLAMMABLE LIQUID STORAGE IN CONTAINERS
This applies to liquids with a flashpoint of less than or equal to 55ºC that will be contained in metal, glass and plastic containers, drums, barrels, tins and Intermediate Bulk Containers (IBCs).
SMALL QUANTITY STORAGE INSIDE
Up to 50 litres of highly flammable liquids may be stored in a fire resisting cabinet or bin, preferably away from the immediate processing area. Normally these bins or cabinets are kept closed and are properly labelled.
It goes without saying that unless actually in use all the individual containers should be kept closed and should also be properly labelled.
Flammable liquids are normally a risk when there is a spillage or leakage. Therefore, it is always preferable to have a storage bin with a hinged lid rather than a cabinet. It is more difficult to make the shelves of a cabinet liquid tight to a spillage and prevent the HFL from seeping out.
EXTERNAL STORAGE
Storage in the open air is the most preferable option for containers of HFL. Drums and containers should be stored on a concrete pad with 1 in 50 slope to one end. This pad should be provided with a sill so that the retention volume is that of the largest container stored.
The sill should be provided with an access ramp for pallet or fork trucks for movement to processing areas or for product despatch. There should be no sources of ignition in the immediate vicinity including that of vegetative growth immediately around the periphery.
The provision of a 2-metre high security fence with locked access gates at the access ramp depends to some extent on the overall security and susceptibility of the site. Such a fence is more likely to be provided than not. If the total travel distance to the exit from the store is greater than 24 metres then a second exit door should be provided as an alternative Means of Escape.
As a general rule of thumb the boundary of such a store should be 4 metres or more from any occupied building, bulk flammable liquid tank boundary or ignition source. If this is not achievable then specifically constructed fire walls will be necessary. -
EXTERNAL STORAGE BUILDING
This building may be freestanding or attached to another building. In both case all walls should be of brick or concrete block construction. The roof should be lightweight so that it may act as an explosion relief but any internal fire would be vented upwards.
Ventilation is important so that there should be high and low level airbricks at 1 metre centres with the bottom of the lower airbricks being above door sill height. Door sill height, as above, is determined by retention volume and the largest container stored.
If glazing is provided it should be non-opening and be of wired glass and be of substantial construction so that it doesn’t act as an explosion relief in default. It is preferable to use natural lighting as opposed to artificial internal lighting. If the latter is the case then clearly it must be protected to an appropriate standard. It would be an advantage for the light switch to be on an external wall.
If the internal floor is part of an existing building of more than one storey then the fragile roof alternative is not available. There should be complete vertical and horizontal fire separation to half-hour standard on common walls and ceilings. Explosion reliefs would be required to be placed on external walls, venting to safe places. Alternatively, local exhaust ventilation could be provided to deal with an anticipated leak but this is a technical matter that would have to be quantified.
There should preferably be no door between the internal flammable liquid store and the remainder of the building, unless size dictates the need for an emergency exit.
ZONE CLASSIFICATION
Zone 2 is defined as being an area in which an explosive gas-air mixture is not likely to occur in normal operation, and if it does occur, will exist only for a short time. That being so, the inside of the store room, whether in an existing building or external building and the inside of any cupboard or bin will be Zone 2. Zone 2 should also be applied to a theoretical volume in open-air storage areas which extends 1 metre vertically above the highest container and horizontally 1 metre beyond the bund or sill.
FURTHER INFORMATION
Reference is made to HSG51 entitled “The Storage of Flammable Liquids in Containers” ISBN 0 7176 1471 9. -
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- 9 - High
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Hand Painting with flammable liquids (Select yes to see guidance)
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Hand Painting with flammable liquids?
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HAND PAINTING WITH FLAMMABLE LIQUIDS
Hand painting is most likely to occur where the standard of finish is not critical and the article is wood or metal. Examples that readily spring to mind would be minor damage repairs on transport vehicles, the painting of one-off metal fabrications or repairs to wooden office furniture.
As the area being covered is much smaller than if spray guns were used, the amount of solvent being released will also be significantly smaller. However, sources of ignition will not be as well controlled and the employees closer to the point of application.
Toxicity and application of the COSHH Regulations will be as important as containing the flammable risk. For example the Lower Explosive Limit of the solvent would be in the order of 2% whilst the Occupational Exposure Limit could be in the order of .02%.
Therefore the LEL would be exceeded only very close to the surface being painted unless the evaporating solvent was allowed to accumulate in a sump or drain.
Keep the quantity of paint being used to a minimum. Ensure good local ventilation and keep sources of ignition away. Do not paint over drainage gullies or equivalent. -
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Spraying with the flammable liquids (Select yes to see guidance)
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Spraying with the flammable liquids?
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SPRAYING WITH FLAMMABLE LIQUIDS
HAZARD
If spraying is carried out in a workshop where someone is smoking or there are other sources of ignition then the vapour will ignite causing a fire or explosion. The HSE lists the following causes of incidents associated with spraying as follows:
- Lack of awareness of the properties of flammable liquids
- Smoking
- Hot work on or close to spray equipment
- Unprotected electrical equipment
- Spillage during handling and cleaning
- Leakage from damaged or poorly maintained pipes, hoses and other fittings
- Flammable overspray deposits on surfaces
- Contaminated cleaning racks
- Inadequate design and installation equipment
- Inadequate inspection and maintenance
METHODS OF OPERATION
Spraying will normally be carried out in the following:
An open front spray booth large enough to take the component with the operator standing outside and directing the spray onto the component and past the component to the extraction system
A walk-in booth for larger components where the operator or operators stand just inside the entrance of the booths but may in some circumstances have to walk round the component being sprayed although this is undesirable
Spray enclosures which are effectively rooms and are usually used for the complete spraying of vehicle bodies or similar structure -
EXTRACTION FLOW RATES
In each case the aim is to provide exhaust ventilation which firstly ensures that in normal operation the concentration does not exceed 25% of the Lower Explosive Limit and also, so far as is reasonably practicable, controls the exposure of the operator to the paint solvents under the COSHH Regulations.
It is usually accepted that a face velocity of 0.7m/s (140 ft per minute) should be available at the front of the spray booth but if there is significant risk of bounce-back this should be increased to 1m/s
If the spraying is done in an open-fronted walk-in booth or a spray enclosure then the airflow can either be from front to back or from top to bottom (down-draught) but the aim here must be to achieve as close as possible to a laminar flow. A good rule of thumb to work for here would be 0.5m/s (100ft per minute).
CONSTRUCTION OF BOOTHS, ENCLOSURES AND SPACES
The structure of the above must all be half-hour fire-resisting to parts 20 and 22 of BS476.
The internal surfaces are all required to have a flame spread and heat classification of Class 0 which is defined in Approved Document B issued in connection with the Building Regulations 1991.
Where the enclosure is a complete spray space or room then alternative means of escape must be provided at diametrically opposite points. Both should be outward opening, fire resisting and the one not the normal exit should be labelled with the Fire Exit pictogram. If the main access door is a sliding door then a small outward opening fire exit should be provided immediately adjacent to that. -
EXTRACTION SYSTEMS
The first part will be the filtration system which will either be a water scrubbing spray or dry filter system that is usually replaceable being made of pleated paper or fibre. The emissions themselves may be subject to the need for an Authorisation under the Environmental Protection Act 1990 depending on the scale of usage, making it a Prescribed Process.
The extraction fans must have a capacity which is defined by the required flow rate and the physical dimensions to be scoured. Having flameproof or protected motors in the ducting is not acceptable as even these are capable of overheating. Therefore the fans must either be bifurcated or centrifugal but there is no reason why the fan itself should not be a normal axial-flow fan which is belt driven with the motor external to the system.
It may be possible to argue that if an axial-flow fan with a flameproof motor is positioned in a wall aperture (and guarded) rather than being confined within ducting then that might be acceptable as the concentrations would never be high. However, this would only apply to small scale use.
The ducting system as with all such systems should be designed to be readily removed for cleaning purposes; pop-riveted metal sections would not be acceptable. The above requirements for fire integrity and flame spread would also apply.
ZONES
A logical approach would be to define all internal volumes where spraying is undertaken as being Zone 1 and defining Zone 2 as an area 2 metres horizontally around the containing structures in any direction (spray vapours are heavier than air).
However, the clever approach would be to ensure that all electrical equipment is external. In the case of lighting this can be in simple sealed enclosures shining through wired glass. Conventional electrical equipment can therefore be used with considerable cost savings. The switches should be more than 2 metres horizontally on the outside of the structure.
REFERENCES
HSG178 ISBN 0 7176 1483 2 entitled The Spraying of Flammable Liquids -
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Handling of flammable solids (Select yes to see guidance)
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Handling of flammable solids?
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HANDLING OF FLAMMABLE SOLIDS
BACKGROUND
Organic and metallic dusts are capable of exploding with considerable violence with pressures of 8 to 10 bar being generated. The average brick wall will collapse at 0.2 to 0.3 bar.
Particle size, oxidation, moisture content and ignition energy are all the variables that would affect the actuality of an explosion. Assuming ready availability of oxygen the particle size is probably the most important where the particles must be less than 120 microns and possibly even less than200 microns (1µm = 1 micrometre. 200µm = 0.2 milimetres). Examples of dusts which explode violently are as follows:
Aluminium
Zinc
Magnesium
Titanium
Resin
Rubber
Coal
Sugar
Grain
Flour
The worst explosions which occur are called secondary explosions and result from poor process controls and therefore fallout of dust into the structure of the building. A primary explosion in an item of plant will shake the building and the residual dust then falls from the high ledges. This descending cloud of considerable volume is then ignited by the residue of the primary explosion and it is this secondary event which causes the catastrophic damage.
PROCESSES
Organic materials, especially in the food industry, are handled in very large volumes. To do so effectively the moisture content must be low. At all stages dust clouds are possible, whether in warehouses, grinding or milling plant, bucket conveyors, storage vessels or in the dust collectors of dust control systems.
Metal dusts are generated in significant quantities in all major industries from aerospace through to metal recycling. The processes can be machining, grinding, granulating or fragmentising. Unless the industry is deliberately creating the dust or powder such as aluminium ball-milling, the metallic dust is a by-product of the process. If properly controlled it will still represent an explosion risk in duct work and dust collectors. If not, there is the potential for the secondary explosion described above. -
PRECAUTIONS
The obvious precaution is to prevent flammable dust clouds above the lower explosive limit from forming. There is no reason why production rate or rate of conveyance cannot be engineered so that the concentration never exceeds 25% of the LEL.
Keep all surfaces as clean as possible. It should be remembered that the finest dust and therefore the most potent, settle on the highest levels. The HSE says that a layer of dust 0.3mm deep can give rise to a flammable cloud 3 metres high. Make the plant leak-proof and where process considerations render this impossible, provide effective Local Exhaust Ventilation.
Control the sources of ignition but much of this goes hand-in-hand with a high level of preventative maintenance. It is important that tool pieces do not break off and be sucked into the extraction system and hence into the dust collector. Equally, bearings and critical parts of plant such as fan casings must not be allowed to overheat.
It is possible to exclude oxygen by inerting but this is always a very costly option and can only be applied in specialised situations.
Dust conveying and collecting systems need to be precisely sited and protected. See D.10.
There may be situations where conventional explosion venting for a number of reasons would not be acceptable. The first alternative is containment where the plant itself is so strong that it would withstand any explosion pressures and one example of this is the hammer chamber of a fragmentiser. This strength could be relied upon if there were other reasons that prevented the fitting of explosion reliefs. Equally, explosion suppression has been available for many years. As regards this control a suppressant medium is available within the vessel. The detection will respond to a pressure rise and snuff out an explosion before it can fully develop.
As well as ensuring that critical plant is in a safe place and explosion reliefs vent to safe places or are deflected, there are many simple design features that can be installed in plant handling flammable dusts. These involve the use of rotary valves and chokes in conveyor systems. The aim is to prevent the transfer system within the plant of continuing to spread burning material.
POST-EXPLOSION FIRES
Many post-explosion situations leave small piles of burning material around the scene. There is a tremendous temptation for both employees and emergency services to blast these with water.
To give one example, if a cone of burning aluminium powder is sprayed with water, it will lead to a violent hydrogen explosion which will then have a significant knock-on effect. In these circumstances the best policy is to leave the material to burn out but if it is felt that some action should be taken then it should be restricted to the careful application of dry sand.
REFERENCE
Further information may be obtained from HSG103 ISBN 0 7176 0725 9 entitled “Safe Handling of Combustible Dusts”. -
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Dust collection system (Select yes to see guidance)
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Dust collection system?
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DUST COLLECTION SYSTEMS
BACKGROUND
Although the heading above refers to dust, this section could equally refer to solvent extraction systems as regards plant protection.
All collection systems will consist of the capture hood or equivalent, the conveying ducting, possibly a cyclone centrifuge depending upon volume and finally a filtering or scrubbing system.
The capture velocity and conveying velocity within the ducting will be determined by the necessities of the process. The dust laden air will be thrown tangentially into the cone of the cyclone with the heavy particles subsequently dropping to the bottom collection system with the partially cleaned air emerging through the top. When considering 5 micron particles the collection efficiency at this stage is between 40 and 70%.
The next stage is a bag filter unit in which air is fed into a container in which there are a series of fabric filters. The fan extracting the whole system extracts from inside these fabric cylinders so that the dust then clings to the outside of the fabric. The collected dust is then shaken free by either a mechanical or pneumatic method with the dust dropping down to a collection bag at the bottom of the unit. Collection efficiencies as high as 99.9% are achievable. The alternative would be a liquid scrubbing system using either a Venturi scrubber or a water spray giving collection efficiencies at 90%. Here the dust is collected as a sludge rather than in the dry state.
The ducting is usually made of steel between 1.6mm and 2.5mm depending on diameter and the aim should be to achieve a velocity of the order of 20m/s in order to prevent dust dropping out within the ducting at its twists and turns and hence causing a blockage. -
POTENTIAL FOR EXPLOSION
Unless it is known that the dust being conveyed is, and always will be, totally inert, then the plant must be protected against the effect of explosions. This refers not only to the ducting but also collecting and dry filtration plant. All the processes mentioned in Section 4 will be capable of generating explosive dust mixtures.
Even in the case of a car fragmentiser whilst it could be argued that fluff and general dust that is being extracted will be inert, tins of thinners or flammable gas cylinders are often hidden within the scrap car and it should be borne in mind that 1 gallon of thinners can generate 9000 cubic feet of flammable volume should it be dispersed throughout the extraction system.
EXPLOSION PROTECTION
There are traditional rules of thumb that have stood the test of time as regards the extent to which plant may be protected. If the explosion is not to be suppressed then the expanding explosion must be vented to atmosphere.
This is achieved by the fitting of explosion reliefs which can take several forms from bursting panels to hinged covers. The key standard is the ratio of the relief to the potential exploding volume. For plant up to 30 cubic metres the ratio of vent area to enclosed volume is 1m2/6m3 (or 1ft2 for every 20ft3). This ratio would be halved for materials such as aluminium and starch which explode very violently.
For plant over 300m3 the ratio becomes 1m2/25m3 and for any plant between these two extremes the ratio will be adjusted proportionally.
The rule of thumb is that the explosion relief must be effective at a pressure of 5psi. In the case of ducting it is usual to fit an explosion relief equivalent to the cross-sectional area of the ducting every 3 metres.
In the case of tall cylindrical storage vessels it is normal to make the top out of explosion relief segments and therefore the positioning of equipment on the top will be critical.
REFERENCES
HSG103 ISBN 0 7176 0725 9 entitled “Safe Handling of Combustible Dusts”. -
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Sources of ignition and hot work (Select yes to see guidance)
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Sources of ignition and hot work?
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SOURCES OF IGNITION AND HOT WORK
A means of ignition is an essential part of the fire triangle. If this is excluded then no matter what amount of oxygen or fuel there is, the combustion or explosion does not take place (this comment does not apply to exothermic and unstable substances).
Common sources of ignition include:
Unprotected electrical equipment
Hot work
Naked flames
Faulty electrical equipment
Friction
Impact sparks
Static
Smoking
Heating to auto-ignition temperature
Most of the above are location-specific and the appropriate controls can be applied. The ones that are not are the control of smoking and hot work which can in fact occur anywhere. If flammable liquids are being stored and manipulated and if there is the possibility of explosive atmospheres then smoking would automatically be prohibited and any breach of that control would be a very serious disciplinary matter. However, hot work is an ongoing necessity in most industrial situations. The simple use of hot work such as removing projecting steel from concrete floors or repairing guard rails can usually be done within the controls of a Hot Work Permit.
However, where complicated isolation procedures are necessary then a full Permit-to-Work procedure will be necessary before a Hot Work Certificate is issued. -
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Gas freeing and inerting (Select yes to see guidance)
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Gas freeing and inerting?
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GAS-FREEING AND INERTING
Bulk storage of flammable liquid (see Section 1), when they are full of a flammable liquid, do not pose a problem as regards explosive atmospheres. It is only when the tank has been emptied that the problem exists. The emptying of the tank could be for maintenance purposes or for disposal.
A large horizontal storage tank with a diameter of 4 metres and 6 metres long would only need a few litres of flammable liquid to exceed the Lower Explosive Limit and it is obvious that when tanks are emptied they are never completely so.
Even tanks which have been open for a long period of time and are effectively completely dry and proved to have no explosive vapour present could contain solid residues. When heated, these residues will give rise to vapours which could then create the flammable atmosphere.
CERTIFICATION
Certificates can be issued to show that a tank is gas-free. Gas-freeing is the process whereby purging has removed any trace of flammability, toxicity or oxygen deficiency to allow entry. These Certificates have a limited period of application, say 24 hours, and cannot be taken to be sufficient for the application of heat.
Steam cleaning is a process by which all solid and liquid residues are removed to a point at which confidence can justify a Naked Lights Certificate. -
INERTING
It has been said that if approximately one-third of a tank top is removed then the danger of explosion is substantially diminished. This is difficult to do and it may be appropriate to modify the atmosphere in the tank over a short period of time to either render the tank safe for repair or for removal and transportation. Each technique has its problems:
- Water Filling
The easiest way to inert a small tank and one benefit is that a flammable gas detector is not required to check on the internal atmosphere. However, the tank may not be designed to take the hydrostatic pressure and the water, possibly contaminated, will have to be disposed of afterwards.
- Carbon dioxide
This is added to reduce the oxygen content below 5%. This is either done from gas cylinders or by adding dry ice at the rate of 2kilograms for each cubic metre of tank capacity. The problems are those of ensuring universal distribution of what is effectively a cold gas throughout the tank and possibly generating static whilst jetting in the carbon dioxide.
- Inert Gas Generators
These would not normally be available but if they are, they are capable of producing a non-combustible mixture in which the oxygen content is about 1%.
- Nitrogen
Nitrogen may be used in the same way as carbon dioxide, again to achieve an oxygen level less than 5%.
- Foam
The tank could be filled with a high expansion foam which may be an air foam or a nitrogen foam. The latter is the preferred method as there is a question against air foams being able to stop flame propagation. -
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Storage and use of compressed flammable gases (Select yes to see guidance)
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Storage and use of compressed flammable gases?
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STORAGE AND USE OF COMPRESSED “FLAMMABLE” GASES
BACKGROUND
There are a large number of gases used in industry that are only available if they are either compressed in cylinders or are liquefied in tanks. These gases fit the definitions of dangerous substances and examples are:
Acetylene R5 Heating may cause an explosion
R6 Explosive with or without contact with air
Butane R12 Extremely flammable
Propane R12 Extremely flammable
Oxygen R8 Contact with combustible material may cause fire
The fact that something may cause an explosion if heated or if released would cause an explosive atmosphere does not mean that it is explosive as defined otherwise it would have the risk R2 or R3 attached.
There is a duty under Regulation 7 for the employer to classify workplaces where explosive atmospheres may occur. However, Schedule 2 to the DSEAR Regulations says:
“A place in which an explosive atmosphere is not expected to occur in such quantities as to require special precautions is deemed to be non-hazardous with the meaning of these Regulations”.
Unless subsequent HSE ACOPs specify otherwise it would seem reasonable to interpret this as meaning that flammable gas cylinders and cryogenic tanks need not be identified as areas where explosions can occur.
STORAGE
The preferred storage for gas cylinders and bottles is in the open air. This provides the best ventilation and makes it easier to obtain sufficient separation distances from boundaries and buildings. The compound should have a lockable 1.8 metre high fence to give security. There seems to be a desire to separate oxygen cylinders from other cylinders. However, mixed storage is permitted to include LPG cylinders. However, once the amount of stored LPG exceeds 50 kilograms then there has to be a physical separation of 3 metres between the LPG cylinders and other compressed gases. If the compound results in a travel distance of greater than 12 metres to an exit then a second exit to the compound is necessary. It is logical to exclude all electrical equipment from the area and rely on high level lighting.
BULK STORAGE OF LPG
The tanks will have been installed to standards specified by the LPG ITA. Confirmation of that will need to be part of the Risk Assessment. These standards will cover the location, separation, mechanical integrity, fittings, piping and vaporisers and security. -
SAFE USE OF GAS CYLINDERS
The correct equipment must be fitted to gas cylinders by your suppliers including non-return valves, flashback arrestors, pressure regulators and the appropriate gauges but much of the inherent safety in the use of cylinders containing flammable gases will be the way in which they are treated.
1 - Handling of Cylinders
The rules in handling cylinders are as follows:
- Wear appropriate PPE which may extend to hand, foot and eye protection according to the Risk Assessment.
- Never lift a cylinder by its valve equipment or guard.
- When moving cylinders any distance use a suitable cylinder trolley. “Milk churning” requires skill and is only possible over short distances.
- Never use a cylinder with a magnet or chain sling. If ropes or lifting straps have to be used, lift one cylinder at a time.
- Never roll cylinders along the ground. This damages both identification and the valves.
- Always shut the valve before moving a cylinder on a trolley and never transport cylinders with the regulator and hose attached unless it is on a purpose designed carrier.
- When handling, do not subject cylinders to mechanical shocks.
2 - Cylinder Checks
Many of these are common sense but include:
- Gas leak checks using a detection solution such as soapy water or 1% Teepol.
- Check that appropriate provision is made for fire fighting.
- Make sure that the gas system that you are connecting to the cylinder is appropriate in all its parts.
- Make sure pressures gauges are the right ones for the particular gas and have the correct pressure range.
- Check the hose colour and quality against the precise standard recommended by your supplier. Always use permanent clips.
- Do not use hoses which look worn and always use the correct coupling devices.
- Only use standard length hoses. If occasionally a long hose is necessary use only recommended coupling devices. -
3 - Abuse of Cylinders
All cylinders are dangerous. The following should never occur:
- The use of gas cylinders as rollers to transport heavy sections.
- Never use direct flame for any heating to raise the pressure of the cylinder.
- Never subject any cylinder to a temperature over 45ºC.
- Never recompress one cylinder from another.
- Never attempt to transfer gases from one cylinder to another.
- Never permit oil, grease or paint or similar substance to come into contact with oxygen cylinder valves.
- Never attempt to repair or modify cylinder valves or devices.
- Never allow electric arc welding tools to come near cylinders.
- Do not allow welding sparks and slag to make contact with cylinders.
- Never use anything but the recommended cylinder valve keys and never attempt to increase the leverage of keys.
- If you suspect that a cylinder valve is damaged, do not attempt to obtain gas from it.
USE OF LPG
The use of the LPG gas, once delivered for use in its gaseous as opposed to liquid form will need to be risk assessed but on the assumption that the delivery mains are to LPG ITA Standards the topic is best risk assessed according to the item of plant that the gaseous LPG is serving. This could be anything from profile cutting machines through to hot mill furnaces or simply space heating.
As with most fixed services it is probably the maintenance element where there will be greatest risk.
REFERENCES
- LPG ITA(UK) Code of Practice No 1 entitled “Installation and maintenance of bulk LPG storage at consumer premises”.
- LPG ITA(UK) Code of Practice No 22 entitled “LPG Piping – System Design and Installation “.
- HSG34 “The Storage of LPG at Fixed Installations” -
Existing control measures?
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Severity
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Risk rating
- 1 - Low
- 2 - Low
- 3 - Medium
- 4 - Medium
- 6 - High
- 8 - High
- 9 - High
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Actions
Action Number :
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Details of action
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Responsibility
Dispensing petrol (Select yes to see guidance)
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Dispensing petrol?
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DISPENSING PETROL
The storage and possible subsequent dispensing of petrol has become an issue as a result of the ELV Directive and the consequential development of decontamination rigs.
The effects of the DSEAR Regulations are as follows:
The HSE will be responsible for the DSEAR Assessment up to the point of storage.
If there is any dispensing of petrol the Petroleum Licensing Officer will be responsible for the DSEAR Assessment to cover storage and dispensing.
If there is no dispensing then the HSE will cover storage as well.
THE HAZARD FROM PETROL
Petrol is given the Category “Extremely Flammable”. It readily evaporates at all ambient temperatures and has a Lower Explosive Limit of 1% in air.
The vapour is heavier than the air and does not disperse in still air conditions. It accumulates readily in any low level cavities or drains. If it gets into water it will float on the surface and be carried long distances. -
RISK ASSESSMENTS
The factors to consider are:
- Control of sources of ignition within a 4-metre radius (smoking, mobile phones, hot work, engines running).
- Standard of dispenser (BS7117 or EN equivalent).
- Small containers being filled and stored elsewhere on site.
- Control of flammables in the area.
- Control of Contractors.
- Overstretching of dispenser hoses.
- More than 4 metres from the site boundary.
- Good illumination.
- Maintenance inspection programme for all equipment.
- Spillage not to go into the site drainage system.
- Sand provided for minor spills.
- Fire fighting equipment dedicated to the dispensing area.
- Training of employees to dispense, and also to deal with minor spills and emergencies.
There may be other control factors that are included as part of the Petroleum Licence.
REFERENCE
HSG146 Dispensing Petrol - ISBN 0 7176 1048 9 -
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- 1 - Low
- 2 - Low
- 3 - Medium
- 4 - Medium
- 6 - High
- 8 - High
- 9 - High
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Action Number :
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Responsibility
Battery Charging (Select yes to see guidance)
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Battery Charging?
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BATTERY CHARGING
There are two different types of lead/acid and alkaline rechargeable batteries:
Valve-regulated (‘maintenance-free’)
In these batteries, any hydrogen and oxygen produced during charging does not escape but is converted back into water. You cannot add water to these batteries, as they do not need topping up.
Vented Batteries
These allow any hydrogen and oxygen produced to escape into the surrounding atmosphere. They require regular topping up with water.
Hazards
Chemical:
Batteries are usually filled with solutions (electrolytes) containing either sulphuric acid or potassium hydroxide. These very corrosive chemicals can permanently damage the eyes and produce serious chemical burns to the skin. Sulphuric acid and potassium hydroxide are also poisonous if swallowed.
The lead, nickel, lithium or cadmium compounds often found in batteries are harmful to humans and animals. These chemicals can also seriously damage the environment.
The gases that come out of a vented lead/acid battery during charging often contain a fine mist of sulphuric acid. Take care to avoid breathing these fumes, and wear suitable eye protection. -
Explosion
Hydrogen and oxygen are usually produced inside a battery when it is being charged. A source of ignition – for example, a flame, a spark, a cigarette or any hot object, electrical equipment, a mobile phone – will often cause mixtures of these gases to ignite and explode. The explosion is often so violent that it shatters the battery and produces a highly dangerous shower of fragments and corrosive chemicals.
Hydrogen and oxygen are produced more quickly as the battery gets close to being fully charged. If you continue charging after the battery is fully charged, a lot of gas will be produced, greatly increasing the risk from explosion.
During charging, gas bubbles often become trapped inside the battery. The mixture of two parts hydrogen to one part oxygen produced is perfect for an explosion. When a vented battery is moved, the trapped gases are released into the air around the battery. A tiny spark is all that is needed to ignite the gases. If this happens in a confined space (e.g. inside the battery, or in an enclosure or a poorly ventilated battery room), a violent explosion is likely.
Valve-regulated (‘maintenance-free’) batteries are much less likely to release hydrogen than vented batteries. However, it is still important to take care when charging them. Gas pressure may build up inside the battery if it is charged too quickly or for too long. If this happens, the pressure relief valves in the battery may open and let the gases escape. An explosion is likely if this happens close to an ignition source.
Making and breaking connections
Many explosions happen when batteries are being connected or disconnected. The sparks produced when this is done incorrectly may cause the battery to explode, especially if it has just been charged.
The correct way of making and breaking connections to batteries is as follows:
- Isolate the battery by turning off all the switches in the circuit. If the battery is in a vehicle, turn off the ignition switch as well.
- If the battery consists of a number of smaller connected batteries (cells), shroud the other terminals to prevent short circuits or flashovers when disconnecting the cells.
- Disconnect the earthed terminal of the battery first. On most vehicles, this is the terminal attached to the chassis, usually by a short, thick wire. In modern vehicles, the negative terminal (-) of the battery is earthed, but always check to make sure.
- Ensure that the connectors and terminals are clean and secure. Reconnect the earthed terminal last.
Do not rest metal tools on or near the battery. If they fall across the battery terminals, they will cause a short circuit. -
Charging Batteries
Explosive gases are given off when batteries are charged. The risk of an explosion is great if the gases are allowed to collect. When charging batteries, follow the procedure below:
Getting ready
- Make sure you understand the battery manufacturer’s instructions on charging.
- Always use a dedicated, well-ventilated charging area.
- Do not smoke, carry out hot work (e.g. welding, brazing, grinding), or use a mobile phone in the charging area.
- Do not charge batteries below electric lights or other equipment that could be an ignition source.
- Check that the charging equipment is suitable for the battery, e.g. correct voltage and charging rate.
Charging
- Raise the lid or open the doors of the battery compartment before starting to charge the battery. This will help to prevent an explosive mixture of gases building up.
- Before starting to charge a vented battery, check that the electrolyte level is just above the tops of the plates in all the cells. Top up the cells with distilled or deionised water if the level is too low.
- Make sure the charger is switched off before connecting the charging leads to the battery (unless the charger manufacturer specifies a different procedure).
- Connect the charger’s positive (+) lead to the battery’s positive terminal and the negative (-) lead to the negative terminal.
- Check that the charging leads are securely clamped in position before switching on the charger.
- Never charge the battery faster than the battery manufacturer’s specified maximum charging rate.
- Do not remove or adjust the charging leads while the charger is switched on. Always switch it off first.
- Switch off the charger before disconnecting the charging leads from the battery (unless the manufacturer’s instructions specify otherwise).
- Allow a vented battery to stand for at least 20 minutes after disconnecting it from the charger. Carefully top up the electrolyte with distilled or deionised water to the manufacturer’s recommended level.
- Store the charging leads so that the uninsulated parts do not rest against each other or any earthed metalwork. This will prevent short circuiting if the charger is switched on suddenly. -
Existing control measures?
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- 1 - Low
- 2 - Low
- 3 - Medium
- 4 - Medium
- 6 - High
- 8 - High
- 9 - High
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Actions
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Details of action
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Responsibility
Other Actions
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Permits to work? (Section 1 for guidance)
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Is Zoning required (Section 2 for guidance)
Section 1
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DANGEROUS SUBSTANCE
This is:
A substance or preparation (ie mixture) which meets the criteria in the Approved Classification and Labelling guide for classification as a substance or preparation which is explosive, oxidising, extremely flammable, highly flammable or flammable, whether or not that substance or preparation is classified under the CHIP Regulations [Chemicals (Hazard Information and Packaging for Supply) (Amendment) Regulations 1998].
The substance or preparation which because of its physico-chemical or chemical properties and the way it is used or is present in the workplace creates a risk, not being a substance or preparation falling within a) above.
Any dust, whether in the form of solid particles or fibrous materials or otherwise, which can form an explosive mixture with air or an explosive atmosphere, not being a substance or preparation falling within a) or b) above.
EXPLOSIVE ATMOSPHERE
This is a mixture, under atmospheric conditions, of air and one or more dangerous substances in the form of gases, vapours, mists or dusts in which, after ignition has occurred combustion spreads to the entire unburned mixture.
CHIP REGULATIONS
These Regulations, amongst other things, define risk phrases which are attached to substances or preparations. The relevant risk phrases in the relevant categories are as follows.
EXPLOSIVE
R2 – Risk of explosion by shock, friction, fire or other sources of ignition.
R3 – Extreme risk of explosion by shock, friction, fire or other sources of ignition.
OXIDISING
R7 – May cause fire.
R8 – Contact with combustible material may cause fire.
R9 – Explosive when mixed with combustible material.
FLAMMABLE CLASSIFICATIONS
R10 – Flammable.
R11 – Highly flammable.
R12 – Extremely flammable.
R15 – Contact with water liberates extremely flammable gases.
R17 – Spontaneously flammable in air. -
OTHER PHYSICO-CHEMICAL PROPERTIES
R1 – Explosive when dry.
R4 – Forms very sensitive explosive metallic compounds.
R5 – Heating may cause an explosion.
R6 – Explosive with our without contact with air.
R7 – May cause fire.
R14 – Reacts violently with water.
R16 – Explosive when mixed with oxidising substances.
R18 – In use, may form flammable/explosive vapour-air mixture.
R19 – May form explosive peroxides.
R30 – Can be highly flammable in air.
R44 – Risk of explosion if heated under confinement.
APPROVED SUPPLY LIST
If, for whatever reason, there is not a label attached to the substance or a data sheet provided, then the risk phrase for the substance can be tracked down via the Approved Supply List which lists in great detail substances and preparations together with the appropriate risk phrases.
REFERENCES
L100 Approved Guide to the Classification and Labelling of Substances and Preparations dangerous for supply. ISBN 0 7176 1726 2.
L124 Approved Supply List. Information approved for the classification and labelling of substances and preparations dangerous for supply. ISBN 0 7176 1832 3.
Section 2
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PERMITS-TO-WORK
A Permit-to-Work system is a formal written system used to control certain types of work which are identified as being potentially hazardous. It is also a means of communication between the management system and the supervisors and operators and even contractors who carry out the hazardous work.
Examples of situations where Permits may be used are as follows:
- A number of trades or a number of separate contractors working separately on an item of process plant which generally will be fairly extensive.
- For ensuring that an item of process plant has been isolated from its services and feed stock, for example electricity, steam, automatic flooding systems, pneumatic delivery and so on.
- Where time is a critical factor of the work and permit is time limited.
- Where entry into a particular work area or workspace depends upon a number of guarantees such as gas-freeing (see Section 8)
- Where hot work is to be undertaken and the issue of a Hot Work Permit is not sufficient to guarantee controls.
- Where other peripheral controls must be in place such as externally applied extraction equipment, airline respirators, harness and rescue line and so on.
It is obvious that any site which stores, processes or applies flammable liquids or generates explosive atmospheres of any type then there will be some diagnostic, repair or preventative maintenance work that will probably involve the application of Permit-to-Work procedure. If there are a wide range of situations, it may be possible for the employer to design a Permit-to-Work so that it satisfies all extremes of the operations of the site.
It is not a good idea to have more than one Permit-to-Work system. Equally, it is not a good idea to use a Permit-to-Work system to try and control frequent operations that occur several times a day simply because other management controls are lacking.
REFERENCE
Guidance on Permit-to-Work systems in the petroleum industry. ISBN 0 7176 1281 3.
Section 3
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ZONING
Once the Risk Assessment has determined that there is a place where an explosive atmosphere may occur in such quantities as to require special precautions, then the action required is as follows:
A black and yellow triangle carrying the legend EX must be fixed in the area.
The area has to be classified. The classifications are as follows:
Zone 0
A place in which an explosive atmosphere consisting of a mixture of air of dangerous substances in the form of gas, vapour or mist is present continuously or for long periods or frequently.
Zone 1
A place in which an explosive atmosphere consisting of a mixture of air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.
Zone 2
A place in which an explosive atmosphere consisting of a mixture of air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but if it does occur, will persist for a short period only.
Zone 20
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously or for long periods or frequently.
Zone 21
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally.
Zone 22
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short time only.
The Regulations add further to the above by indicating that layers, deposits or heaps of combustible dust, such as aluminium powder around granulators, must be considered as any other source that can form an explosive atmosphere and in terms of the above “normal operation” means the situation when installations are used within their design parameters. -
ELECTRICAL EQUIPMENT
Unless the Risk Assessment finds otherwise, the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmosphere Regulations 1996 require that certain categories of equipment must be used. These are as follows:
Zone 0 or Zone 20 – Category 1 equipment.
Zone 1 or Zone 21 – Category 1 or 2 equipment.
Zone 2 or Zone 22 – Category 1, 2 or 3 equipment.
Advice on such equipment must come from a specialist supplier.
