Causes and prevention of fi re
8.4 Prevention of fi re
8.4.5 Chemicals and LPG (hazardous materials) The vast proportion of chemicals used in the workplace
are classifi ed under CHIP and therefore fall under the Control of Substances Hazardous to Health Regulations (COSHH). These chemicals together with liquefi ed petroleum gas (LPG) may also fall under the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), each of which requires the effective manage-ment and control of risk.
When considering the management of chemicals and LPG, formalised procedures must be produced, implemented and monitored in relation to their use, storage, transportation and disposal.
Appropriate training in all areas including the handling of chemicals and LPG gas cylinders is critical to securing the safety of all those in the workplace and others who may be affected.
Figure 8.15 Halogen lighting unit fi tment
Causes and prevention of fi re
The principles of safety relating to both chemicals and LPG are similar in many ways and it is intended to consider these overall principles for each hazardous material as one, with specifi c areas of difference being highlighted.
Substitution
Ideally the use, storage, etc. of fl ammable chemicals and substances and LPG should be avoided where rea-sonably practicable. The same can be said for using low fl ashpoint liquids. Other chemicals, substances or liquids, which are either non-fl ammable or have a higher fl ash-point, may provide suitable safer alternatives.
It must also be noted that reactive chemicals whose properties in themselves are non-fl ammable, but may react violently even explosively when mixed together, should also be considered in relation to substituting them for less reactive materials.
Storage
Where substitution cannot be accommodated, the provi-sion of safe storage must be considered as a key elem-ent in reducing the fi re and explosion risks from the hazardous materials.
Ideally, arrangements should be made for storage of fl ammable liquids, gases and substances to be stored well away from other processes and general storage areas. This is most effectively achieved by a physical distance. An alternative approach may be to provide a physical barrier such as a wall or partition, combined with a storage system or container.
If the storage facility is to be located within a building and the hazardous materials are to be handled within the area around the store fi re resisting separation from other areas of the building or workplace should be considered.
The arrangements for storing fl ammable substances and LPG will depend upon the storage facilities avail-able, the amount of hazardous materials and the nature of the materials.
External storage arrangements – when storing large quantities (50 litres or more) ideally an external storage area will be provided that will include the follow-ing considerations:
➤ Segregation from other processes and storage (fl ammable substances should be stored separately from other hazardous substances and materials such as oxidisers and LPG, etc.):
➤ By physical distance
➤ Fire wall
➤ Security against unauthorised access, locking mechanisms, physical walls and fences
➤ Positioned in a well-ventilated area and on impervi-ous ground
➤ Take into account the potential heat on the con-tainers from a fi re within or outside the premises’
boundary; and a fi re within the storage facility on buildings, plant and people inside or outside the premises
➤ Positioned away from sources of ignition (or where electrical supplies are intrinsically safe)
➤ Environmental protection arrangements:
➤ Bunded facility (110% of contents)
➤ Interceptors to capture potential release
The acknowledged safe separation distances are detailed in Table 8.3.
The arrangements for the storing of larger quantities (more than 300 kg) of LPG gas cylinders are very similar to those required for fl ammable liquids.
In addition to providing adequate levels of signage on site, formal systems of work will need to be Figure 8.16 External tank facility
Quantity stored Distance from occupied
litres building, boundary, process
unit, fl ammable liquid storage tank or fi xed ignition source metres
Up to 1 000 2
1 000–100 000 4
Above 100 000 7.5
Table 8.3 Minimum separation distances
developed and implemented that:
➤ Keep rubbish and anything combustible well away from the cylinders, and keep weeds and grass in the vicinity cut down (avoid using a chlorate-based weedkiller, as it can be a fi re hazard in itself)
➤ Prevent any electrical equipment, vehicles, bonfi res or other sources of ignition near the cylinders
➤ Prevent smoking when changing cylinders
➤ Prevent people not involved with the storage or installation gaining access to it, particularly children (construction sites particularly)
➤ Keep vehicles well away from the installation (fi re and impact hazard)
➤ Protect against accidental damage, ensuring that pipework is properly routed and supported. In the case of underground routing that schematic dia-grams of the pipe routes are drawn up, to avoid putting anything in the ground which may damage the pipework
➤ Enable reports of any equipment failure or damage to the supplier without delay.
Internal storage – where fl ammable substances can be stored within specially designed separate buildings, safe by position, the same control measures as those required for outdoor storage, with the additional require-ment that the building should generally be constructed of non-combustible material and the roof of the building be of lightweight materials, may be used. The roof would open readily to release the effects of an explosion, there-fore acting as explosion relief.
Ventilation of any building used for a fl ammable material store must also be considered; the ventilation apertures or bricks must be so positioned to allow air fl ow within the building/store and must be positioned at both high and low level. The apertures must not be sited so that they allow ventilation to other buildings or to external areas that could contain ignition sources. The number of apertures (based upon the total fl oor area in per cent) required will depend on the substance stored, e.g. 1% fl ammable liquid and 2.5% fl ammable gases.
Additional measures would be required for stores that cannot be positioned in separate buildings, particu-larly the fi re resistant separation from other parts of the building as shown in Fig. 8.19.
Figure 8.18 External storage arrangements for LPG Figure 8.17 Example of a well laid out external storage facility for fl ammable chemicals – HSG 140
Maximum stack
capacity 300 000 litres Note:
See Table 8.3 and the text for minimum distances shown by dashed arrows Fire wall
Building
Retaining sill Truck ramp
Fire-fighting
equipment Building Boundary fence
Causes and prevention of fi re
The storage arrangements for smaller amounts of fl ammable substances and LPG will vary dependent upon the processes for which they are being used.
All containers that are to be used to store fl ammable liquids should be designed and constructed to meet the standard of being suitable for the purpose.
Containers also need to be of a performance tested type, in that they should be robust and have well-fi tting lids and spill resistant tops to prevent leakage if knocked over. There are specifi c standards available for such containers and their packaging to comply with transport legislation.
To ensure that no chemical or physical interaction occurs which might cause leakage, the material, from which the containers are made, needs to be compatible with the properties of the liquid. In addition, containers may need protection against corrosion, e.g. by painting, and plastic containers can often suffer degradation by natural light, which can be reduced by suitable shading of the container.
LPG cylinders can also suffer degradation from corrosive atmospheres particularly in relation to some chemical operations, therefore the use and storage of the cylinders should refl ect the workplace conditions and be stored outside.
Storage within the actual workplace where the fl ammable substance or LPG is to be used must be considered at length. Ideally external storage arrange-ments should be made; where this is impracticable the following must be considered:
➤ Keep the quantities of fl ammable materials and LPG stored and used to an absolute minimum
➤ Storage arrangements should be made available for fl ammable liquids which are separate from other substances including LPG – up to 50 litres may be stored within the work area if enclosed in a fi re resisting cabinet or bin
➤ Securing mechanisms should be provided to any storage that allow only authorised access
➤ The storage facility must be provided with spill protection
➤ Flammable liquid containers should always be replaced in the store following use and such con-tainers should be provided with lids to protect against vapour release and spillage
➤ LPG storage (up to 300 kg) should be ideally in open air but must be with good ventilation if stored within a workplace (see Fig. 8.18)
➤ Proprietary safety containers (such as dash pots used in the printing industry) should be fi tted with self-closing lids for fl ammable liquids
➤ Flammable liquids should not be dispensed or decanted within a store or adjacent to a store.
Arrangements for such operations should include the provision of ventilation and extraction systems
➤ The storage facility should be located away from ignition sources
➤ Signage denoting the fl ammable storage facility should be displayed, including ‘no smoking’
➤ An inventory of the substances should be kept including as a minimum the name of the substance, type and quantity kept
➤ Arrangements for the safe storage and disposal of items such as rags, cloths, etc. which may have been used to apply the liquids or mop up spillage.
Figure 8.19 Example of suitable fl ammable storeroom in a building
Lightweight roof
½hr self-closing fire door, with sill
Ventilation apertures
sill
Fire-resisting internal walls
For example, metal containers with tight fi tting self-closing lids and regular removal (end of day/shift) from site.
Training – as discussed at the start of this section, train-ing is a key element for ensurtrain-ing effective management of an organisation’s fi re safety and in particular with regards to fl ammable substances and LPG. Any train-ing programme must cover the arrangements for the safe handling and storage of these hazardous materials, together with the arrangements for the safe disposal.
An outline of such a programme may be as follows:
➤ The types of fl ammable substances in use, their properties and hazards
➤ General procedures for safe handling of substances and operation of plant
➤ Use of personal protective equipment and clothing
➤ Housekeeping arrangements
➤ Reporting of incidents and faults, including spills and minor leaks
➤ Specifi c instructions on individual items of equip-ment, plant and processes
➤ Emergency procedures, including raising the alarm, and use of appropriate fi re fi ghting equipment, deployment of spill kits, etc.
Figure 8.20 LPG cylinder storage facility
HIG HLY
FLAMMABLE
Non-combustible, high melting-point hinges
Maximum 50 litres total Half-hour fire-resistant exterior
Examples of special-purpose containers for flammable liquids
Examples of metal container for cloths contaminated with flammable solvents
Bonded/fire-stopped junction
xxxxx xxxxx xxxxx
Figure 8.21 Internal fl ammable storage facility
Causes and prevention of fi re
Ventilation of storage areas
Ventilation has been discussed as part of the storage requirements; however, all areas where fl ammable liquids are handled should be adequately ventilated to ensure that any released vapours are diluted to a safe level.
Whichever ventilation system is used it needs to be capable of providing a minimum of six complete air changes per hour. The system’s capacity should ensure that the amount of vapour in the atmosphere is not only diluted to well below its fl ammable limit, but also reduced to a level below any relevant workplace exposure limit (HSE’s guidance note EH 40 gives advice on workplace exposure limits).
Dependent upon the concentrations and volumes in use good, natural, well-positioned ventilation may be adequate, but where this cannot be achieved, mechan-ical ventilation and/or local exhaust ventilation (LEV) is almost certain to be needed.
Positive pressure mechanical systems can be used to force air into an area; diluting and venting any potential build-up of fl ammable vapours. Any area provided with a positive pressure mechanical system will also need to be provided with suffi cient openings to release the atmosphere created. LEV systems are designed to capture airborne contaminants such as fl ammable vapours, fi lter them and ventilate outside a building to a place of safety in the open air.
Any vents provided for the release of pressure or contaminants should be a minimum of 3 m above ground level, at least 3 m from building openings, boundaries and sources of ignition, and away from building eaves and other obstructions where they could become trapped. The ducting taking the fl ammable vapours away should be arranged so that they cannot condense and collect at low points within them.
Ventilation/fume cupboards – in certain operations (e.g. solvent-based spraying operations or decanting of fl ammable liquids) booths or cabinets are required to control the build-up of fl ammable vapours. In such instances the airfl ow rate into all openings in the enclosure should be suffi cient (about 1 m/s) to prevent vapours entering the work area. These ventilation booths, cabinets and other enclosed equipment are generally designed to ensure that the vapours are kept below 25%
of their LEL.
As the outcome or failure of any ventilation system or part of the system may result in a build-up in vapour concentrations with the potential for both fi re and explosion, the system must be provided with an alarm system to provide warning.
There are also a number of storage systems that are combined with booths and cabinets which use LEV for vapour control. Regardless of the system used each must be subject to rigorous maintenance testing and examination regimes to ensure that fl ammable vapours are controlled.
Any electrical system used as part of the ventila-tion or extracventila-tion systems must meet rigid electrical standards and as in the case of all such equipment be intrinsically safe. As discussed earlier, classifying hazardous or potentially explosive atmospheres is not only a legal requirement under DSEAR but has been widely used to determine the extent of hazardous zones created by fl ammable concentrations of vapours.
Over recent years the process of classifying hazard-ous areas in such a way has been extended from its initial purpose of selecting fi xed electrical equipment for use in the area, to helping to identify and eliminate potential ignition sources, including portable electrical equipment, vehicles, hot surfaces, etc. from fl ammable atmospheres.
Wind direction
Figure 8.22 The use of wall and roof vents together, give
good natural ventilation Figure 8.23 Example of a fume cupboard
This zoning has assisted, for example, in identifying that vehicles such as forklift trucks used for transport-ing containers of fl ammable substances, which operate within classifi ed areas/zones inside and outside storage buildings, must be protected to an appropriate standard – particularly during storage operations, when the highest probability of a release from a container occurs while it is being mechanically handled. Therefore an unprotected forklift truck may well provide a source of ignition should a breach of containment occur.
The management of works that involve the removal, replacement or disposal of any part of a plant or system that has previously held fl ammable liquids, materials or LPG must be planned and undertaken with great care, to avoid fi res and explosion.
Many such works will be carried out under the Construction, Design and Management Regulations, utilising specialist contractors undertaking works as part of a permit to work system – PTW (see section on construction and maintenance) to ensure the highest level of management control.
Various techniques can be employed to ensure that fl ammable substances are managed effectively includ-ing purginclud-ing or inertinclud-ing the system prior to undertakinclud-ing operations. Ensuring that residues are removed and that any supply system has been isolated from both power sources and process materials must also be undertaken as part of the systems of work and the PTW.
Disposal arrangements for contaminated fl amma-ble materials and aerosol cans, empty fl ammaamma-ble liquid containers or gas cylinders must also be considered.