A DHA is a systematic review of where combustible dust is generated, where it accumulates, what could ignite it, and whether the safeguards in place actually manage each scenario. We deliver it as an engineering document, not a checklist.
For a decade, combustible dust compliance meant working across a stack of documents. NFPA 652 carried the fundamentals, and five commodity specific standards sat alongside it: NFPA 61 for agricultural and food processing, NFPA 484 for combustible metals, NFPA 654 for general manufacturing, NFPA 655 for sulfur, and NFPA 664 for wood processing. They overlapped, and working out which one governed a given process was a real part of the job.
NFPA 660, Standard for Combustible Dusts and Particulate Solids, consolidated all six into one document. The 2025 edition took effect on 6 December 2024. Chapters 1 through 10 are fundamentals that apply to every facility handling combustible particulate solids, including hazard identification, the dust hazard analysis itself, management systems, prevention and mitigation, and a new chapter on emergency planning. The commodity specific requirements begin at Chapter 21.
If a process handles, generates or accumulates a combustible particulate solid, the obligation attaches. In Ontario that commonly means:
A dust collector on a combustible dust is also item 2 in the Table to section 7 of Ontario Regulation 851, which means the same equipment frequently triggers a Pre-Start Health and Safety Review at the same time. We routinely run both together so the plant pays for one mobilisation instead of two.
A DHA that has not been anchored to measured explosibility data is guesswork. We coordinate sampling and laboratory testing, then work from the numbers:
Kst places the dust in a St class: St 1 up to 200 bar·m/s, St 2 from 201 to 300, St 3 above 300. The class governs how much vent area a vessel needs and whether venting alone is a defensible protection strategy.
We work compartment by compartment through the process, not building by building. For each one we document the dust involved, the quantity, the conditions under which a cloud can form, and every credible ignition source.
Where the analysis identifies an unprotected deflagration hazard, the mitigation work sits under two companion standards that NFPA 660 did not absorb.
NFPA 68 governs deflagration venting: vent area calculated from Kst, Pmax, vessel volume and vessel strength, plus the vent discharge path. On indoor collectors the vent path is usually the harder problem. A correctly sized vent discharging into an occupied space is not protection.
NFPA 69 covers explosion prevention: chemical suppression, mechanical isolation with fast acting valves, rotary valves qualified as isolation devices, flame front diverters, and oxidant concentration reduction. Isolation matters because ducting propagates a flame front from the collector back into the process faster than most people expect.
Ducting and air conveying design also falls under NFPA 91, and any return air arrangement needs looking at carefully. Electrical equipment in a dust environment is classified under NFPA 70 and the Canadian Electrical Code.
Send drawings or photographs and we will tell you plainly whether a review is required, before any fee is discussed. We work across all of Ontario.
For anything specific to your equipment, call 613-983-2642.