Alert: Thermal spray aluminum coating process
Learn about installing and maintaining dust collection and ventilation systems to minimize or eliminate the chance of an aluminum dust explosion.
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Thermal sprayed aluminum (TSA) is used to protect materials against corrosion. It is generally applied by either electric arc or oxy-fuel flame spraying, using solid metal wire. The TSA coating may be applied either in a shop or in the field (on-site). Thermal spray applications have been used in industry for many years; however, industry reports indicate an increased use of on-site TSA application (mainly on construction projects).
The explosive hazard associated with aluminum dust is well documented. A dust explosion can occur when combustible dusts are suspended in air and are ignited. A number of conditions must be met for a dust explosion to occur:
- The dust must be combustible and release enough heat when it burns to sustain the fire.
- The dust must be capable of being suspended in air.
- The dust must have a particle size capable of spreading the flame.
- The concentration of the dust suspension must be within the explosive range.
- An ignition source must be in contact with the dust suspension.
- The atmosphere must contain sufficient oxygen to support and sustain combustion.
- There is a form of confinement or enclosure that allows pressure to build.
Requirements under the Occupational Health and Safety Act and suggested precautions
The process of applying TSA creates fine aluminum dust. Dust control measures must be implemented to minimize or eliminate the chance of an explosion, including the installation and maintenance of appropriate dust collection and ventilation systems.
Where a process that is likely to produce a gas, vapour, dust or fume that is capable of forming explosive mixture with air is carried out in an industrial establishment, section 63 of Regulation 851 (Industrial Establishments) under the Occupational Health and Safety Act (OHSA) must be complied with. Section 63 requires that the process be carried out in an area which has provision for safe disposal by burning under controlled conditions, or that the process be situated separately from other operations and have adequate ventilation to ensure a hazardous concentration is not reached. No potential sources of ignition are permitted in areas of an industrial establishment where there are potentially explosive concentrations of a gas, vapour, dust or fume. Section 63 also requires that the separately situated area must have provision for explosive venting and, where applicable, have baffles, chokes or dampers to reduce effects of any explosion.
Section 65 of Regulation 851 sets out requirements for a collector that collects aluminum dust. It requires that the collector be outdoors or that it be in a room used solely for housing the dust collector which is separated from the rest of the building by a dust-tight partition having a minimum fire-resistance rating of one hour and constructed to provide explosion venting to the outdoors.
Where section 7 of Regulation 851 applies, the dust collection system must be reviewed and/or designed by a Professional Engineer (P. Eng.) to ensure that all hazards are adequately addressed. Protection against ignition sources, including static energy, must also be implemented, as aluminum dust is easily ignitable. Consideration of water infiltration or condensation is also important, as hydrogen gas can be produced as a by-product of a reaction of water with aluminum dust.
Prevention of cross-contamination with other metal dusts is also important. For example, thermite may be generated as a result of mixing iron oxide (rust) and aluminum dust. Thermite can be a source of intense heat which can burn the skin and thus requires personal protective equipment for skin protection as required by section 84 of Regulation 851.
Failure to appropriately maintain equipment, including a dust collection system, can also result in injuries to workers and/or explosions.
Exposure to aluminum dust is a respiratory hazard and the airborne concentration must be controlled to be in compliance with the exposure limits prescribed in the Regulation for the Control of Exposure to Biological or Chemical Agents (Regulation 833). Appropriate respirators may be required to be worn by workers if engineering controls are not adequate to control the exposure.
Generation of ozone and/or carbon monoxide, radiant heat, ultraviolet (UV) light and high noise levels is also possible during TSA application. Section 2 of the Noise Regulation, O. Reg. 381/15 sets out the requirements for protecting workers from exposure to hazardous sound levels.
The TSA process in the field presents unique challenges because of the potential for condensation of water on the product, or water in the area in which the TSA process is being performed. On-site application usually involves enclosing the area with tarps (‘tenting’) and applying various methods to control the collection of aluminum dust. Lighting and electrical equipment must be appropriate for use in hazardous areas as specified in the Ontario Electrical Safety Code. The security of the enclosure should be assessed to ensure that dust does not escape into areas where an explosion or fire could occur.
In addition, the following general provisions in OHSA and its regulations may also apply to situations where the TSA process is used:
- Maintenance – The employer shall, under clause 25(1)(b) of the OHSA, ensure that the equipment provided by the employer is maintained in good condition.
- Training and Supervision –The employer shall, under clause 25(2)(a) of the OHSA, provide information, instruction and supervision to a worker to protect the health or safety of the worker.
- Hazard Awareness – The employer shall, under clause 25(2)(d) of the OHSA, acquaint a worker or person in authority over a worker with any hazard work and in the handling, storage, use, disposal and transport of any material or chemical.
- Training re: Personal Protective Equipment – As required by section 79 of Regulation 851, a worker required to wear or use any protective clothing, equipment or device must be instructed and trained in its care and use before wearing or using the protective clothing, equipment or device.
- Skin Protection – As required by section 84 of Regulation 851, a worker’s skin is to be protected by wearing apparel sufficient to protect the worker’s skin from hazards.
Other legislative and regulatory requirements
Adherence to other requirements such as those found in the Fire Code, Environmental Protection Act, or the Ontario Electrical Safety Code would also be applicable.
- NFPA 652 Standard on the Fundamentals of Combustible Dust
- NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
- NFPA 484 Standard For Combustible Metals
- NFPA 68 Standard on Explosion Protection by Deflagration Venting
- The Aluminum Association “Guidelines for Handling Aluminum Fines Generated During Various Aluminum Fabricating Operations” designated F-1
For more information
This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations, and should not be used as or considered legal advice. Health and safety inspectors apply and enforce these laws based on the facts they find in the workplace.