Page 19 - OHS, January/February 2021

Assessing Dangers of Dust Explosions
ThThere are many ways to detect dangerous dust explosions before a problem occurs. BY DR. ASHOK GHOSE DASTIDAR
COMBUSTIBLE DUST
Dust explosions are a serious haz- ard in the process industries. They have led to the destruc- tion of property and damage to
facilities and equipment. In the worst cir- cumstances, they may also lead to injury of plant personnel and even fatalities. In 2017 alone, there were 68 globally reported cases of dust explosions with 163 injuries and 13 fatalities.1 They are not as common as flam- mable vapor or gas explosions, but they do occur often.
With the potential for such a dangerous workplace hazard, the reader may assume that there are federal and state laws in place protecting worker safety. However, there are currently no laws in place at the state or federal level protecting workers against dust explosion hazards.
Nevertheless, there are consensus standards developed by the National Fire Protection Association (NFPA) that pro- vide detailed guidance for preventing and mitigating dust fires and explosions. These guidelines are considered to be widely ef- fective. Fortunately, the standards are voluntary unless they have been adopted by a municipality or state as local code. The NFPA dust codes are mentioned in the International Fire Code as well as the
Uniform Fire Code, which are globally acknowledged model codes that various governments base their own local, state and national fire codes upon.
Due to this, the NFPA dust standards are considered recognized and gener- ally accepted good engineering practices (RAGAGEP). Worker safety organiza- tions and insurance companies then use these standards as safety guidelines for plants and facilities. OSHA used these standards to establish their own Combus- tible Dust National Emphasis Program (CPL 03-00-008) back in 2008 and have successfully enforced them through the use of the General Duty Clause OSHA Act of 1970 section 5(a)(1). The clause states that “each employer shall furnish to each of his employees’ employment and a place of employment which are free from recog- nized hazards that are causing or are likely to cause death or serious physical harm to his employees.”
Anticipating Dust Incidents
Five factors are required for a dust ex- plosion to occur. Often, these factors are arranged pictorially in a pentagon to fa- cilitate hazard analysis and investigation. Figure 1 depicts an Explosion Pentagon
and the five factors that are required for a dust explosion.
Fuel. The material at your facility—ei- ther a resource, a product or byproduct— that when present in sufficient quantities can sustain combustion.
Oxygen. This can come from either the air or another chemical oxidizer in unique circumstances.
A credible ignition source. This can be an open flame, electrical/electrostatic spark, hot surface or mechanical spark, etc.
These first three components taken to- gether constitute a Fire Triangle and can be used to look for fire hazards at the facility. It is the addition of the last two factors that elevate the event to an explosion.
A credible mechanism for the dis- persion of the dust into a cloud. This fa- cilitates rapid combustion, which increases heat and pressure development from the oxidation/combustion reaction.
Confinement. The enclosure for the suspended dust cloud where pressure, due to rapid combustion, can increase until a violent failure occurs. This final violent failure can be in the form of an exploding dust collector, storage silo, dryer, mixer or even a building.
Industry Specific Standards
There are five industry specific dust stan- dards:
■ NFPA 61 is for agricultural and food industries.
■ NFPA 664 deals with woodworking facilities.
■ NFPA 484 covers metal dust fires and explosions.
■ NFPA 655 encompasses sulfur han- dling industries.
■ NFPA 654 is for chemicals, poly- mers, resins and pharmaceuticals.
Governing these five industry specific standards is NFPA 652, which is a core fun- damentals rule that applies to all industries if one of the specific industry standards does not apply to your facility.
There are three objectives for NFPA 652. The first is “Life Safety” to ensure that all persons are protected against the adverse
www.ohsonline.com
JANUARY/FEBRUARY 2021 | Occupational Health & Safety 15