Paint spraying in industry is performed on a range of products, from small, individual articles to car bodies on a continuous production line. In this article, Dr Roger Bentley focuses mainly on the small-scale and occasional processes, discussing good and bad practices.
The hazards associated with paints and solvents are toxicity and flammability. These do not vary, irrespective of the scale of the operation. The risks, however, do ― and not necessarily in proportion to the quantity of chemicals used. The reason for this is that the large-scale applications may be fully-automated, or at least done in purpose-designed spray booths (or cabins) by trained personnel wearing high-quality protective clothing and equipment. On the other hand, the small articles and one-off jobs are sometimes performed without any proper facilities, and little protective equipment. Risk assessments must be carried out in all circumstances, to comply with the Dangerous Substances and Explosive Atmospheres Regulations 2002, and with the Control of Substances Hazardous to Health Regulations 2002.
Solvents contained in paints often have acute effects on the central nervous system, initially causing giddiness and then, with further exposure, unconsciousness. The paints may also contain other hazardous chemicals, such as chromates, that are carcinogenic, or isocyanates that are respiratory sensitisers leading to asthma. Developments in paint formulations have, in many other applications, seen the substitution of highly flammable solvents with aqueous formulations, or at least with less flammable organic solvents. Likewise, the use of many toxic chemicals, such as lead compounds, has been eliminated except for some very specialised purposes.
However, the technology of spray coating still entails the use of flammable solvents and paints with toxicity issues, especially in relation to asthma. So both the safety and health of paint sprayers need to be considered. Unfortunately, even the use of small amounts of paint can present a high risk in either case, and that is sometimes not appreciated by those who perform or condone work without adequate precautions. For example, in car body repair work, a drive-in booth may be available for respraying an entire vehicle, but when a small item is all that needs touching up, it is common to find the spraying being carried out elsewhere in the workshop. Even if the painter is wearing adequate respiratory protection, colleagues working on other tasks in the vicinity may be unacceptably exposed.
Spray booths and spray rooms
Spray booths are designed primarily for extracting the vapours evaporating from the sprayed surface, together with any aerosol of the paint that remains in the atmosphere. The flow of air can be either from the front to the back of the booth, or downwards through grills in the floor. In either case, the air has to replaced, either by introducing fresh, filtered air, or by recirculation after treatment. The published standard relating to this is BS EN 12215:2004 + A1:2009, which sets the minimum airflow required to ensure that the concentration of flammable material in the atmosphere is reduced below the lower explosive limit (LEL) everywhere other than in the immediate range of the spray gun. Paint should be sprayed in the direction of the extraction. Where the item is to be sprayed on more than one side, it helps if it is placed on a turntable, so enabling it to be turned around.
Spray booths are also designed to avoid sources of ignition, with equipment powered by compressed air rather than by electricity, and lighting placed behind sealed transparent panels. Even though the atmospheric concentrations of chemicals can be kept below flammability limits, it does not mean the air is safe to breathe; workplace exposure limits are typically in parts per million, whereas LELs are measured as percentages. So paint sprayers should wear breathing apparatus supplied with fresh air (from a remote compressor or gas cylinder) when working in a booth.
Where space constraints within workshops preclude the installation of a permanent walk-in spray booth, a retractable enclosure is a possibility. Purpose-designed facilities coupled with air-treatment units are now available (see, for example, www.duroair.com). It is not advisable to erect similar tents without considering risks such as the fire resistance of the fabric.
Spray rooms is the name often given to rooms that have been dedicated to paint spraying, but it is rare for them to be kitted out as well as purpose-designed spray booths. Ideally they should be constructed from non-combustible or at least fire-resistant materials. Purpose-designed spray booths may have automatic sprinklers for fighting fires, but these are less likely to be present in modified facilities.
It is possible to use a fume cupboard for a smaller scale of operation, with the painter on the outside. However, if not specifically designed for this type of work, the system requires careful evaluation to ensure that there is not an unacceptable risk of fire. A typical fume cupboard is not usually designed to eliminate potential ignition sources, such as electricity, and even if not immediately visible, these could exist in the ventilation system. It might still be necessary for the painter to have some form of respiratory protection, especially where the paints contain asthmagens.
When the spraying operation is carried out without any extraction, a flammable vapour cloud will develop, perhaps even engulfing the painter. This only needs to reach a source of ignition for an explosion to take place. All hot work in the vicinity would need to be prevented, so ignition sources are not introduced. Even a static discharge could ignite the flammable vapour and mist. In a proper booth, earthing facilities are integral. Personnel should wear “anti-static” shoes and overalls, to prevent static charges building up on their bodies. Also the floor should have a low resistivity to assist with the dissipation of charge.
Another feature of spray booths is that the functioning of the spray gun is interlocked with the ventilation. If the ventilation fails for any reason, then the spraying will automatically be interrupted. Again, such a feature is unlikely with improvised facilities.
Furthermore, operators carrying out spraying without proper facilities are also less likely to have breathing apparatus available. More likely they will use a filter mask. Even if these are of a suitable specification, it does not take long before the filter becomes either saturated with solvent or occluded with paint. Respiratory protection should not be removed immediately after completion of spraying; adequate “clearance time” should be allowed. There is often a temptation to remove a full-face mask that has become contaminated, to check the quality of the painting. Putting a thin film of plastic across the visor of a face mask helps to keep paint off, and can be changed without removing the mask if vision becomes poor. Fit testing of masks is mandatory. Disposable, chemical-resistant (eg nitrile) gloves should always be worn.
Painting outdoors will mean that vapours disperse rapidly, but this is not commonly done as it is difficult to achieve a quality finish due to problems such as dust blowing around.
The actual application of the paint is only part of the job, with mixing of paints often being required beforehand, and cleaning of equipment afterwards. These should not be undertaken in the spray booth, as equipment put there has an adverse effect on the flow of air. Ideally a preparation room, often referred to as a “paint kitchen” should be available. This will have good extraction ventilation; interlocking that with the lighting circuit will ensure it is always switched on when anyone is in the room. Electrical equipment will need to be ATEX-compliant (ie not a source of ignition); lighting is often installed behind sealed transparent panels as a cheaper method. Some of the equipment, eg a shaker for mixing paint, is often pneumatically operated.
Paint guns, of which there are a variety of types designed to minimise paint mist and overspray, with technical names such as “air-assisted airless”, are refined pieces of equipment that need to be well maintained. In particular, these need to be cleaned after every job. This is best done with a specially formulated cleaning solvent compatible with the type of paint in use. These solvents are usually highly flammable liquids. Cleaning baths are available that perform the process in closed equipment, to minimise the amount of vapour getting into the atmosphere. However, some workplaces carrying out just occasional painting may clean them just by rinsing with “thinners” and spraying it through the gun: this should always be done in a place with adequate ventilation. As with the paint application, both flammability and toxicity hazards need to be considered.
Storage and maintenance
Thinners are used both to dilute the paint and for various cleaning methods. Again, the solvents used are usually flammable and may have health effects. Defatting of the skin is often a problem where rags soaked with thinners are being used to wipe up paint. Never use thinners to clean the skin.
It is often the case that a paint kitchen contains more cleaning solvents and thinners than it does paint. Keep the lids on all of them when not in use. Containers should have secondary containment such as standing them within bunds or on sump pallets. The stock of these, and also paint, within the paint kitchen should be kept in fire-resisting cupboards. However, only the necessary stock for immediate use should be retained there, with as much as possible kept in outdoor storage facilities, or if that is not possible then in a suitable indoor storeroom.
Clean-up kits should be at hand to quickly deal with any spillages, and should include absorbent granules to soak up liquid.
Waste disposal needs proper provision of items such as a drum for paint and thinners. Wipes contaminated with paint, and especially those that have been soaked in thinners or cleaning solvent, should immediately be placed in a closed, metal receptacle. Any incompatible components, such as accelerants, need to be kept separate, and that also applies to any waste. Some products may need special treatment, in particular activators containing isocyanates, and may need to be immersed in water or dilute sodium carbonate solution to destroy residual respiratory sensitisers; always follow the manufacturer’s instructions. All need to be disposed of as hazardous waste.
Health surveillance should always incorporate checks of the skin for dermatitis. If respiratory sensitisers are used, then lung function tests should also be carried out. Exposure to isocyanates can also be monitored by assessment of the corresponding amine metabolite in the urine. This is usually performed on an end-of-shift sample.
If an individual develops isocyanate-related occupational asthma, all further exposure must be prevented. Even the smallest amount of exposure could trigger an asthma attack, and fatal consequences are possible.
Training should include how to use, clean and maintain the equipment and personal protective equipment. It should also include information about the properties and effects of the paints and solvents, the need for health surveillance, and what to do if something goes wrong.
Finally, it should be mentioned that there are other hazards associated with paint spraying, including tripping over the hoses, or falling into a pit in a car maintenance workshop. Painters may also encounter musculoskeletal problems, particularly where spraying involves much bending.
Last reviewed 28 January 2014