RDM ENGINEERING, recommends that you obtain, as a minimum, a copy of the booklet HSG 178 available from the
Health and Safety Executive.

RDM will be very pleased to advise on your specific requirements.
Please find below a 'synopsis' of our understanding of the requirements.

The main hazards from the use of flammable liquids are fire and explosion, involving either the liquid or the vapour given off from the liquid. Fires or explosions are likely to occur when vapours or liquids are released into areas where there may be an ignition source, or when an ignition source is introduced into an area where flammable liquids are being used.

Flammable liquids can pose a health hazard if they are ingested, come into contact with skin or eyes, or if their vapours are inhaled.

The Highly Flammable Liquids and Liquefied Petroleum Gases Regulations 1972,16,17 require precautions to reduce the risk of fires and explosions. These precautions include measures to prevent a flammable athmosphere from being formed and to control ignition sources.

Under the Management of Health and Safety at Work Regulations 1992, 18,19 every employer has a duty to carry out an assessment of the risks to the health and safety of employees and of anyone who may be affected by the work activity.

The usual way to control the flammable vapours arising from spraying processes is to use a ventilated spray booth or enclosure. Its purpose is to:

Prevent the escape of vapours into the Workplace
Prevent contamination of the workplace by overspray
Protect the health of workers
Provide separation from sources of ignition and to prevent the spread of fire:
Prevent contamination of the workpiece by dust and grease and from the work environment.
Draw overspray away from the operator.
Control flammable and hazardous vapours.
Collect vapours, droplets and solid particles: and
Filter or wash the air before it is discharged.

There are many different designs of spray booth. The design of the booth will depend on the articles to be sprayed.

A spray booth or enclosure should be of half-hour fire resisting construction. If spraying is carried out in a partial enclosure, a work area or a spray space, then it should be fire separated from adjoining rooms.

The ventilation should be sufficient to prevent the formation of dangerous concentrations of flammable vapours.

The basic parameter used to specify ventilation requirements is the control velocity. This is the air velocity at the operative's position. The control velocity required depends on the spraying conditions. It should be sufficient to overcome turbulent air movements generated by hoth the process and random air currents. It should also be sufficient to draw polluted air away frorn the operator.

A minimum average air velocity of 0.7 m/s at the front of open-fronted booths and enclosures is recommended. If the sprayer works inside a side-draught booth or enclosure, the minimum average air velocity where the sprayer stands should be not less than 0.5 m/s vhith a minimum measured value of 0.4 m/s. Where a sprayer works inside a down-draught booth or enclosure, air velocity (measured at points around a typical article to be sprayed) should average 0.4 m/s with a minimum measured value of 0.3 m/s.

Suppliers of proprietary equipment should advise on the appropriate flow rates for the proposed purpose.

It is advisable to leave the fan running for several minutes after spraying has finished in order to remove vapours from the system effectively. This can be done with a time delay in the control circuit of the fan motor. Wet items should not be left in a booth or enclosure when the ventilation is switched off, such as during lunch or tea breaks or at the end of the working day as a flammable atmosphere may develop.

It is impossible to avoid flammable atmospheres during spraying of flammable liquids and so control of ignition sources is essential. Ignition sources include:

Unprotected electrical equipment;
Heating appliances;
Smoking materials;
Welding and other similar hot work activities;
Sparks generated by the discharge of static electricity;
Iinternal combustion engines.

Ignition sources should be kept out of spraying areas at all times. Even when spraying is not taking place, flammable residues, contaminated materials, drying and cleaning operations may still present a fire risk.

Hazardous area classification is the method used to identify areas where flammable concentrations of gases or vapours are likely to be present. The aim is to reduce to a minimum acceptable level the probability of a flammable atmosphere coinciding with an electrical or other source of ignition. It is normally used to select fixed electrical equipment but it can also be used in the control of other potential ignition sources such as portable electrical equipment. hot surfaces and vehicles.

There are three classes of hazardous area or zone: zone 0, zone 1 and zone 2. A zone is an area around a process or activity where a flammable atmosphere may be present. It is advisable to exclude electrical equipment from the spray area.

Any electrical equipment that has to be inside the spray area should be designed and constructed for use in a zone 1 or zone 2 according to the hazardous area classification. All other sources of ignition should be removed from the hazardous area.

Zone 0 An area in which an explosive gas mixture is continuously present or present for long periods.

Zone 1 An area in which an explosive gas mixture is likely to occur in normal operation.

Zone 2 An area in which an explosive gas mixture is not likely to occur in normal operation, and, if it does occur, is likely to do so only infrequently and will exist for a short period only.

For spray areas, the zones depend on where spray gun may be used, the level of ventilation, the output of the spray gun, the flashpoint the spray and its vapour density.

In many cases a qualitative or 'common-sense' assessment will be sufficient. For example. everywhere in range of the spray gun should be considered as zone 1. For spray booths, the simplest approach is to regard the whole booth interior as zone 1, and to exclude all electrical equipment and other sources of ignition. Adequate lighting of the interior of the booth may be achieved either by using protected lighting, or by allowing light from an overhead fitting to shine through half-hour fire-resistant glass panels sealed into the top of the booth.

Any ductwork should be at least half-hour fire resisting. It should be as short as practicable and have no sharp bends, as this tends to decrease the air flow and allow the deposition of residues. Access points for inspection and cleaning inside the ducts may be needed. Dampers should not be fitted in exhaust ducts unless they are essential for balancing the ventilation system.

Electric motors for fans should not be situated in the path of flammable vapours. This may be achieved using bifurcated, centrifugal-type or belt-driven axial fans. Motors (even if they are of flameproof construction) should not be sited within the ducts.

As a relatively high volume of air will be exhausted, it is important that the room containing the spray process is provided with adequately sized fresh air inlets.

Flammable vapours are also released during the drying process and may present a serious fire hazard. The drying conditions will depend on the type of coating, some will dry at room temperature, others may need curing or baking at higher temperatures. For drying at room temperature, the spray booth or a designated drying or 'flash-off ' area may be used. Ventilation should be provided to prevent the build-up of flammable vapours.

Ovens are used for drying or curing at higher temperature. They may be separate or combined with a spray booth (combi-booth). They should be ventilated to prevent the build up of flammable vapours. Some are designed to recirculate a proportion of the warm (solvent laden) air. It is important to ensure that the dampers are positioned to maintain an adequate exhaust flow rate. The vapour concentration may be monitored with gas detectors which trigger an alarm, emergency ventilation and shutdown, if the concentration exceeds a specified level.

Explosion relief should be properly maintained: it should be covered, obstructed or nailed down. It should vent to a safe place.

Following the advice on this webpage will help to reduce the risk of a fire occurring. Unfortunately, the possibility of fire always remains. It is important to have a pre-planned response to such emergencies, including the appropriate actions to be taken in the event of a fire. The main aim is to ensure people can escape to a place of safety.

The Fire Precautions Act 1971 requires the following as a minimum:

Escape routes;
Fire extinguishers;
A system of giving warning in the case of fire;
Management procedures to ensure that all of the above are available and maintained, and that there is adequate training in their use.
Means of escape

Fires in spray booths or workshops tend to develop extremely rapidly. There should be adequate means of escape from enclosed, walk-in booths. Operatives should never be more than 6 m from an exit door.

If the booth is located within a workshop or the workshop is a spray area, then there should be adequate means of escape from the workshop. Again, operatives should never be more than 6 m from an exit door. At least one exit door from the workshop should open either directly into open air, or into another part of the building from which there is an exit direct to open air, separated from the spraying area by a fire-resisting construction having at least 30 minutes fire resistance. All exit doors, either emergency or normal use doors, from spray booths or workshops should open outwards.

It is advisable to discuss the installation of a sprinkler system with the fire authority and with the fire insurance company. The fire authority will also need to discuss their requirements for fire fighting such as water supplies and access for appliances.

The above is intended as an introduction and is not a comprehensive document please contact a specialist
Technical Advisor at RDM ENGINEERING for more information.

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