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The advent of fiber laser cutters and flexible manufacturing cells are creating growth opportunities for metal fabrication shops. However, the new processes and heavier demands on growing shops may also increase the potential for a combustion event.
Because metal shops are inherently high-risk environments for combustion, risk mitigation must be a top priority. To manage these hazards, there are three points every shop owner should know:
Guidance for managing combustible dust is provided by the National Fire Prevention Association (NFPA). As industry best practices, these standards are frequently mandated by city, state, and municipal codes, and OSHA has been known to cite them during inspections. A good place to start is to review these three key standards:
Under NFPA Standard 652 (2019 edition), all facilities that produce or handle combustible dust are required to complete a dust hazard analysis (DHA) and risk mitigation plan by September 7, 2020.
The first step in a dust hazard analysis is to identify all dusts and fumes produced in your facility and determine their combustion risk. Laboratory testing may be necessary for this determination. Be sure to review all areas of your operation and all dusts present, including dust and fume mixtures. Metals that are stable in one process can be volatile when oxidized or mingled with other metals.
Because metal fires can be very challenging to extinguish, NFPA 484 provides specific guidance, such as:
(See Table A.6.3.3 in NFPA 484: Combustible Metal Fire-Extinguishing Agents Quick Reference Chart.)
A fire and explosion risk management strategy should consider both preventive and protective measures. Prevention methods help reduce the likelihood of an ignition, while protective methods are intended to limit the damage if one occurs.
You can integrate many of the following mitigation options into your new or existing dust and fume collection system. The combination you choose may depend on factors such as your risk tolerance level, downtime concerns, and resources.
Housekeeping — NFPA 484 requires that metal dust be removed from the dust collector at least daily and possibly more often, depending on the process. Also, schedule regular housekeeping of facility surfaces to reduce dust accumulation. Be careful to clean out-of-sight areas, because an initial explosion can suspend hidden dust and trigger a larger secondary event.
Collector Location — Locate your dust and fume collector outside your facility, if possible. NFPA standards require this for some dust types. An outdoor location gives you additional mitigation strategies. For example, a fire in an outdoor collector, properly isolated, could be allowed to burn itself out.
Dedicated Equipment — Separate volatile and reactive metal dusts from each other. If you work with multiple types of metals, consider dedicating dust collection equipment to each process. Point-of-use dust and fume collectors can help accommodate this strategy. Ensure you label your dedicated dust collectors and train employees on appropriate use.
Spark Control — Prevent sparks from reaching the fuel source (dust) in the collector. Sometimes, distance (longer duct) between a potential spark source and collector is sufficient. However, because air velocity is high through a dust collection system (up to 4,500 cfm), very long lengths of duct may be necessary for this to be effective. A good alternative may be a passive spark arrestor – a device that creates turbulence to accelerate the rate at which sparks extinguish in the duct before they can reach the collector.
Explosion Venting — Specialized panels are installed on a dust collector and are designed to break open during an explosion, venting explosive materials into a dedicated safe area or “exclusion zone.” Note that equipment controls should not be located within this zone.
Explosion Supression — This equipment senses rising pressure in the dust collector and sets off a chemical suppressant to halt a combustion event. Although more expensive, explosion suppression devices are very effective at stopping initial as well as secondary events.
Isolation — Isolation devices are used to limit the impact of a deflagration to the dust collector. There are many types of isolation devices and strategies, depending on your dust types and facility layout. Be aware that deflagrations involving metals can grow faster than some equipment can react, so consult with the device manufacturer about appropriate selection for your application.
Fire Extinguishing System — Choose a fire extinguishing system that is compatible with your metals and processes. Water-based systems may be lower in cost, but can require significant clean-up. Carbon dioxide or argon-based systems may allow for faster recovery, but potentially at a higher cost.
Manufacturing facilities processing combustible metals needs to understand their risks and develop an appropriate mitigation strategy. The DHA process helps metal shop owners address these risks early and may help reduce the likelihood and consequences of a combustion event. By knowing what your combustible dust is, where it occurs, and how to mitigate the risks it presents, you can develop a mitigation strategy that supports new growth opportunities.