Combustible dust poses a significant threat of fires and explosions in industries such as manufacturing, distribution, and handling. Tiny particles of dust, of 420 microns or smaller in diameter, are easy to ignite and in some circumstances can contribute to explosions.
Understanding the Risks: What Makes Dust So Dangerous?
The Dust Explosion Pentagon: A dust explosion occurs when five key elements are present: combustible dust in a dispersed cloud, oxygen, and an ignition source (e.g., spark, flame, hot surface), confinement in an enclosed or semi-enclosed space, and dispersion in the air to form a cloud. Understanding this “explosion triangle” is the first step in preventing these incidents.
Particle Size: Smaller particles are particularly hazardous because they have a high surface area to volume ratio. Only the surface of a thing can burn, because that is what is exposed to oxygen, so because dust has a lot of surface area for its mass, they are very easy to ignite, disperse, and burn very rapidly. Combustible dust is defined as any finely divided solid material 420 microns or smaller [NFPA 654-1994].
The Impact: Incidents with dust can cause catastrophic damage to property, equipment, and, most importantly, result in serious injuries or fatalities. This is particularly true when dust is confined in an enclosed space because rapid combustion can lead to a dangerous pressure buildup, resulting in an explosion. The U.S. Chemical Safety and Hazard Investigation Board (CSB) identified 281 combustible dust incidents between 1980 and 2005 that led to the deaths of 119 workers, injured 718, and extensively damaged numerous industrial facilities.
NFPA 660: The Standard for Combustible Dust Safety
In order to decrease the chances of a fire or explosion happening in high-risk industries, The National Fire Protection Association 660 standard for combustible dust address the risk of fires and explosions. This standard mandates that the facility owner must take the appropriate actions to prevent fires and explosion where combustible dust is or may be present. Compliance is essential to protect the people in these working environments, as well as prevent devastating damage. In jurisdictions that have adopted the 2018 International Building and Fire Codes, compliance with NFPA 652 is legally required and this means that a dust hazard analysis is mandatory. While these regulations may seem burdensome, they are essential for ensuring workplace safety.
Dust Hazard Classifications
The class scale ranges from st0 to st3 and indicates varying degrees of explosibility, with st0 being no explosivity and s4 being the highest class for explosivity. The KSt value refers the rate of pressure increase as a dust explosion occurs. A higher Kst value means it will rank highly on the explosion class scale.
The severity of a combustible dust explosion is also dependent on many other variables, such as the size and shape of the dust particles, moisture content, ambient humidity, available oxygen, and the concentration of dust in the air.
Material with a low explosion class can still cause catastrophic incidents if other variables create the right circumstance. For example, the West Pharmaceutical Services explosion was caused by a buildup of polyethylene powder which only has a ST 1 explosion class. The tiny particles of plastic had accumulated above a suspended ceiling in the production area, and when ignited by an unknown source, the buildup causes a chain reaction of fires and explosions which led to 6 fatalities and 36 people injured.
Dust Hazard Analysis
The Dust Hazard Analysis is a valuable tool used for NFPA 652, to improve safety and prevent fires and explosions by identifying combustible dust hazards. The facility in question is reviewed and evaluated to determine where fires and explosions are likely to occur due to combustible dust. Each of the areas is individually evaluated to determine its specific hazards. After determining the appropriate hazards, prevention plans are constructed to minimize or alleviate the risks. Dust Hazard Analyses should be reviewed and updated at a minimum of 5 years, as well as whenever there is a change or update to a facility since new hazard areas can occur during these changes.
Get in touch if you want to keep your facility safe and complaint. With a Dust Hazard Analysis, RAN is able to stay ahead in fire prevention and in protecting buildings and facilities against dust hazards.