Question: What is a combustible dust?

Answer: The Occupational Safety and Health Administration (OSHA) states “Any combustible material can burn rapidly when in a finely divided form. If such a dust is suspended in air in the right concentration, under certain conditions, it can become explosible” ( These dusts can be found in various industries including chemical, pharmaceutical and food, among others.

Question: What is a Dust Hazard Analysis?

Answer: Since 2013, the National Fire Protection Association (NFPA) 654 Section No. 4.2, has required a Process Hazards Analysis (PHA) if there is combustible dust handling in a facility. In September 2015, the NFPA issued the new NFPA 652, Standard on the Fundamentals of Combustible Dust. The new standard, to be enforced by OSHA, requires a Dust Hazards Analysis (DHA) be completed on existing facilities where combustible dust is present within three years, September 2018. It also requires the completion of a DHA on new facilities.

The DHA concentrates on potential risks for a dust explosion by reviewing each piece of equipment and each compartmented area in the facility where dust is present. It then evaluates if the conditions required for deflagration are present. If conditions are not present, this is documented so future modifications can be compared for increased risk. If conditions that could support deflagration are present, recommendations for design requirements are made to mitigate the risk or eliminate the condition. The end goal of a DHA is improved plant safety.

Question: PHA vs. DHA; what’s the difference?

Answer: A PHA is a more complex analysis of the equipment and operations design which handles hazardous materials. If a unit or facility is covered under OSHA 1910.119 (Process safety management of highly hazardous chemicals) a PHA is required under that section. Within the new standard, the DHA is required to be separately documented and would then be used to inform the PHA.

Question: Who performs a DHA?

Answer: NFPA 652 7.2.2 states that “The DHA shall be performed or led by a qualified person.” This does not require any specific certification, however, does require familiarity with combustible dust and executing DHA’s. The DHA will likely be a team of two or more depending on complexity. Per the standard, the team may include “facility operators, engineers, owners, equipment manufacturers or consultants.”

Question: What information is required for a DHA?

Answer: The first step, if you have not already done so, is to test any potentially combustible dusts to determine the ease and severity of an explosive condition. A reputable testing lab should test your material for Kst, Pmax, and MIE. Be sure to test ingredients, intermediates and final products. The results of this testing will be required to effectively complete a DHA.

Design information from your processes is also necessary. This is normally information that is readily available such as P&ID’s, equipment specifications, equipment layouts, and building layouts.

Question: Would a DHA be required in the Pharmaceutical industry?

Answer: The pharmaceutical industry often encounters combustible dust through processes such as milling, pressing, and coating. While the processes are enclosed, they still pose a risk to employees, equipment and the facility if the design is not to standard. With the completion of a DHA, processes and conditions are reviewed to ensure they are operating at safe levels, or recommendations for modifications are made as appropriate. In many cases, housekeeping levels in a pharmaceutical plant will minimize the risk, but a DHA will shed a light on other risks that might have been overlooked.

If you are interested in learning more about Dust Hazards Analysis and the services we offer, please contact John Koehler.

Author: Ken Koehler, P.E.