Dust Hazard Analysis

Definition

According to NFPA 652 (Standard on The Fundamentals Of Combustible Dust), DHA is A systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility. The DHA shall evaluate the fire, deflagration, and explosion hazards and provide recommendations to manage the hazards in accordance with Section 4.2. (NFPA 652) The results of the DHA review shall be documented, including any necessary action items requiring change to the process materials, physical process, process operations, or facilities associated with the process.

Methodology

The DHA was conducted following the general procedure outlined in NFPA 652. The process(es) and building(s) are broken down into individual components, or nodes. At each location, a series of questions are asked:

  1. Is the particulate deflagrable, suspended in air, and above the Minimum Explosible Concentration MEC?
    In order to have a flash fire or explosion, there must be fuel (deflagrable particulate), an oxidant (usually air), and there must be a large enough quantity of dust suspended in the air (above the Minimum Explosible Concentration, MEC).
  2. Are there competent igniters available?
    Sources of ignition can include open flames, electrical sparks, static discharges, hot surfaces, mechanical sparks, friction, hot work, chemical reactions, propagation of explosion or fire from elsewhere, etc.
  3. What existing hazard management is in place?
    This can include deflagration venting, explosion suppression systems, isolation, ignition source control, maintenance or housekeeping procedures, etc.

Answers to these questions are used to determine if hazards exist, under what conditions they exist, and if the hazards are currently being mitigated in any way.

Applicable Standard

  1. NFPA 652 : Standard on the Fundamentals of Combustible Dust.
  2. NFPA 654 : Standard for prevention of Fire and Dust Explosion from the Manufacturing, Processing, and Handling of Combustible Dust Solids.
  3. NFPA 61 : Standard for the Prevention Fire and Dust Explosions in Agricultural and Foods Processing  Facilities.
  4. NFPA 664 : Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities.
  5. NFPA 499 : Recommended Practice for the Classification of Combustible Dust and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Area.
  6. NFPA 68 : Standard on Explosion Protection by Deflagration Venting.
  7. NFPA 69 : Standard on Explosion Prevention Systems.

Risk Evaluation

To estimate the risk, the consequence and initiating event frequency are combined. The unreliability (probability of failure on demand) of layers of protection is used to modify the resulting scenario likelihood. Methods for combining initiating event frequency, consequence estimates, and probability of failure to obtain risk measures.

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