NFPA 652: Beyond the Dust Hazard Analysis

The plastics industry is replete with powders that, if dispersed in air, will form explosible dust clouds. These powders include the molding compounds, resins, ingredients and fillers used throughout the industry. The files of the Chemical Safety Board contain many plastics industry-related dust fires and explosions.

The National Fire Protection Association (NFPA) has developed detailed standards to help industry identify and manage the fire and explosion hazards of combustible dusts and particulate solid; the 2019 Edition of NFPA 652 is the most recently updated standard. Although it may be a fundamental high-level standard in some ways, it places clear obligations on the owner/operators of facilities that handle or process potentially combustible dusts.

NFPA 652 requires the owner/operator of a facility with potentially combustible dust to take responsibility for the following activities:

• Determine the combustibility and explosibility hazards of materials they handle.

• Identify and assess any fire, flash fire and explosion hazards, or Dust Hazard Analysis (DHA).

• Manage the identified fire, flash fire, and explosion hazards.

• Communicate the hazards to affected personnel.

Yet after a company has collected the data, measured dusts for explosion properties in labs and undertaken a DHA at its facility, the requirements of the standard for procedures and training to "manage the identified hazards" and "communicate the hazards" do not always receive sufficient attention. Here, we will review what you need to do after you have the explosion data and have completed your DHA. Incidentally, the steps required under this heading of "management systems" below apply retroactively. You need to do it now, however long your facility has been operating.

It is important to have written operating procedures and practices that will prevent/mitigate dust explosions and fires. These written procedures should include maintenance and servicing as well as normal operation and need to be implemented by staff and contractors alike. Scheduled walk-throughs to validate practices and compliance are also very important.

Training and hazard awareness for staff and contractors become an important part of NFPA 652 requirements. The training level, frequency and depth will depend on the responsibilities and activities expected of personnel; however, an operator who does not understand how a dust explosion can occur and why certain precautions are in place could be at risk and could put others at risk.

Good housekeeping practices are important since powder layers not only produce large fires, they can also be disturbed and raised into a cloud form that is explosible. Such housekeeping practices must be verified periodically, through a documented audit.

Clearly proper procedures for "hot work" are required, including the risk of ignition of powder layers or clouds by hot surface, welding torch, sparks from cutting, and so on.

Emergency planning and response should feature in post-DHA work. Simple things like using the wrong fire extinguishing medium could actually create a dust explosion out of a fire if smoldering powder is raised though firefighting. And there are some powders where water should never be used to fight fire.

After an incident, an investigation by qualified persons should always be carried out to establish root cause and to develop procedures that ensure a repeat could never happen.