Combustible Dust Explosions: Are You at Risk?
By: Tim Turney, Contributor
Between 1980 and 2005, the U.S Chemical Safety and Hazard Investigation Board (CSB) identified 281 combustible dust incidents that ultimately led to the death of 119 workers and 718 injured workers, on top of extensive damage to the respective facilities. In many of these incidents, both managers and workers were unaware of the associated safety and health risks that extensive amounts of dust in the air posed, with prolonged exposure to airborne dust associated with health conditions such as chronic breathing, lung problems and possibly heart disease.
Combustible dust explosions are one of the largest and most fatal potential accidents when working with materials that produce large quantities of fine dust particles—posing a threat to the health of those working in these environments. For many, coal dust, grain storage and flour mills are immediately associated with dust explosions, as they make primetime news. However, any workplace that generates dust is potentially at risk of dust explosions, including agriculture, woodworking facilities, paper, plastics, textiles and pharmaceuticals. Materials that do not normally burn in larger pieces are also still at risk of becoming explosive in certain conditions, such as aluminum and iron.
What Creates Dust?
Dust is created when materials are transported, handled, processed, polished, ground and shaped. Dust can also form from abrasive blasting, cutting, crushing, mixing, sifting or screening dry materials. The build-up of dried residue from the processing of wet materials can also generate dust.
Levels of dust in the workplace continuously rise from such daily activity, which is why employers need to stay vigilant to the amounts of dust in the workplace to protect workers from hazardous incidents and potentially detrimental consequences to their health.
A dust explosion can only occur when the following five factors are present:
- Combustible dust (fuel)
- Ignition source (heat)
- Oxygen in the air (oxidizer)
- Dispersion of dust particles in sufficient quantity and concentration
- Confinement of the dust cloud
There are several ways dispersion can occur, such as a dry filter being pulse-cleaned or from an initial (primary) explosion in processing equipment, causing a blast wave that disturbs accumulated dust that, if ignited, causes a secondary explosion. The latter is often far more destructive than a primary explosion, due to the increased quantity of dispersed dust.
Employers have been reminded of the importance of efficiently monitoring dust levels from the severity of combustible dust explosions over the last few years. In February 2003, a Kentucky acoustics insulation manufacturing plant suffered several dust explosions because of a small fire from an unattended oven, igniting a dust cloud nearby that resulted in a cascade of explosions throughout the plant. Seven people were killed in the accident; 38 were badly injured.
The following are all contributors to ineffective dust control in an environment:
- Hazard assessment
- Hazard communication
- Maintenance procedures
- Building design
- Investigation of previous fires
What can employers and managers do to protect their workers, and what can workers do to protect themselves from combustible dust explosions?
The Hazard Communication Guidance for Combustible Dusts, 2009, as set out by OSHA, names the requirements needed to improve and safeguard the health and safety of those working around and with dangerous substances. Employers need to identify where explosive atmosphere conditions occur; assess the risk; and record what actions are being taken to prevent an explosion and fire.
One of the most important, life-saving measures that an individual can take to protect themselves is through high-quality dust monitoring equipment. Undertaking a walk-through survey using a hand-held, real-time sampler would give an instantaneous indication of concentration. It could also be used to check the effectiveness of control measures such as local exhaust ventilation, for example, both pre- and post-filter.
Industrial hygienists may already be undertaking personal monitoring for toxic or sensitizing dust. The same air-sampling pump could be used in combination with a real-time sampler when housed in a robust, portable case on an unattended, short-term basis. Such a system can provide concentration using a gravimetric filter but also a time-history profile, which could help identify the source of the problem.
Fixed, AC-powered solutions could also be used continuously for high-risk areas. These have the advantage that the data can be made available remotely using a web-based interface. These systems provide real-time alerts via text message or email should limits be exceeded. Reports can easily be automated and sent to multiple users, which allows early intervention to avoid a potential problem.
Great care should be taken in hazardous atmospheres that may require instrumentation to be intrinsically safe or require a hot-work permit, and action thresholds should always be set at a fraction of the Lower Explosion Limit (LEL) for the dust in question. However, if there is any doubt whatsoever, businesses must speak to the relevant site manager or supervisor that has responsibility for risk assessment and permitting—and who can advise accordingly.
Dust explosions continue to be a persistent problem for many industries, resulting in loss of life, injuries and destruction of property. Even those individuals most highly trained, including government enforcement officials, insurance underwriters and company safety professionals often lack awareness of combustible dust hazards. Material Safety Data Sheets (MSDS) are also ineffective in communicating to employers and workers the hazards of combustible dust explosions and ways to prevent them. This is further reasoning for all employees to have a basic awareness of the hazards of dust explosions and the best way to mitigate those risks.
About the Author
Tim Turney is a Technical Product Manager at Casella and graduated as an engineer from Queen Mary and Westfield in London. Since starting at Casella in 1998, Tim has been involved in the acoustics and air sampling industry, specializing in measurement and instrumentation technologies. To find out more about Casella, please visit www.casellasolutions.com or follow @CasellaHQ on Twitter or @Casella on LinkedIn.