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|1. What is NFPA
|2. What is a DHA ?
|3. How to do a DHA ?
|4. An example of DHA
This page explains the Dust Hazard Analysis requirement of NFPA 652, especially what is a DHA and how to do a DHA.
European factories have since 1994
been obliged to comply with a directive called "ATEX" which was
aiming at identifying and managing explosion risks in factories.
This directive included the gas / vapour explosions which are the
ones that were easily thought (although far from always addressed
properly) by factory operators of but also included the risks
related to the explosion of dust, a hazard much less
recognized and that could lead to severe catastrophes (silo
In US, a similar standard focusing
on combustible dust explosions has been issued by the NFPA : the
standard NFPA 652. This standard is mandatory and
especially requires the completion of a Dust Hazard Analysis
(DHA). The document, as of May 2020, is setting a deadline
to complete the DHA by 7th September 2020 and asks for a review
and an update every 5 years. Not having completed the DHA properly
will result in OSHA citations.
If your company is processing,
handling, creating any kind of dust, then the standard NFPA 652 is
applicable and a DHA must be performed. This does not appear
obviously to plant managers but for example, if you simply have a
cutting process generating some dusts that are aspirated and
collected, then a dust explosion risk can exist and you must run a
Other relevant standard that derive
from NFPA 652 and can be relevant are the following :
Factory operators must check
which standard is applicable to their company and apply then.
A Dust Hazard Analysis (DHA) is a structured approach to identify, then manage (through prevention or mitigation), the risks associated with dusts at different points of the factory. The Dust Hazard Analysis basically is done in 3 steps :
The 1st step of the DHA is to map the production process in order to identify where are potential hazards related to dust fire and / or explosions. It is therefore advisable to perform a DHA with a multidisciplinary team which knows well the working environment and can provide relevant documentation (P&ID, equipment datasheet and drawings...) and which should include a person which has expertise in hazards related to combustible dusts.
The team performing the DHA must then start by gathering explosion data (MIE, MIT, Kst, Pmax...) on the dust handled in the factory, then must be listing the area where combustible dust is present. Once the factory is mapped, the actual hazard must be evaluated.
Combustible dusts are taking fire and / or exploding in specific conditions. The team carrying out the DHA must then check the following :
If the team arrives the conclusion that yes, a combustible powder is in a sufficient concentration / quantity within an oxidant and that a source of ignition can be present, then, there is a hazard, which an be a dust fire or a dust deflagration, and prevention and mitigation actions MUST be taken. The actions will however depend on the level of risk, which can be estimated thanks to a risk assessment matrix.
There can be many safeguards, but the DHA team must make sure that they apply well to the particular dust hazard considered.
For instance, it can be possible to prevent the explosion by removing one of the elements leading to an explosion :
However it is sometimes not possible to prevent reliably an explosion. In this case, the DHA will have to recommend mitigation measures such as explosion panels, suppression systems... etc ... Note that the NFPA standards 68 and 69 may have to be applied during the study.
The conclusions MUST be documented in the DHA and the factory MUST apply the conclusions. It is critical for safety that the risk be properly adressed, an action plan defined and timely executed.
A DHA must be carried out by a multidisciplinary team and must include experts in dust explosion. If the company is large, such expertise can be found within the group, otherwise it is recommended to contact a reputable consultant to support in the process.
Some of the critical concepts required for performing a DHA can be found with the following links
Identification of hazards, material explosion properties
The 1st step of a DHA is to properly collect the different properties of the dust handled. It may be required to carry out specific tests to determine those properties if they are not known or cannot be found in the literature. Defining MIE, MEC, MIT, Kst, Pmax for the ingredients involved is mandatory, other characteristics (resistivity...) may be also required depending on the process.
The plant operator must also gather Pipe & Instrumentation Diagram, layout and equipment characteristics that constitute the production line. Those elements are very important to gauge the risk and define how big are the risk areas in the factory. The documents must be updated so it may require a preparation time to gather and update them prior to starting the DHA.
Analysis of the hazard
The identification of hazards should allow to determine where combustible dust can be present in dangerous concentration and at which frequence. The assessment of the risk should then be completed by checking if an ignition source can be located in the area where the dust is present. A risk assessment matrix is recommended to record and classify the different hazards identified during the analysis.
Table 1 : example of DHA risk
Management of the hazard
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Please follow the link to read an example of DHA
Always remember that Dust Explosion Analysis are mandatory, and conclusions of the risks analysis must be implemented by the factory.