The hazards of dust accumulation in the workplace have been a safety and health concern for many years. There have been many production facility explosions and fires that were directly related to dust accumulation, causing serious injuries and loss of life, not to mention property losses. With recent citations from the Occupational Safety and Health Administration (OSHA), it has now become a hot issue in the pallet industry.
The two major safety concerns involving dust accumulation in the workplace are:
• Employee health and safety concerns from dust exposure
• Fire and explosion hazards from combustible dusts
Employee Health and Safety Concerns from Dust Exposure
Airborne particles of organic and non-organic materials can cause health related issues from long-term exposures. Everything from skin irritation to lung cancer, respiratory exposure to dusts from either organic or non-organic substances is of the highest concerns when it comes to employee health. According to the American Thoracic Society, most types of lung disease can be caused by work exposures including: asthma, chronic obstructive pulmonary disease (COPD), interstitial lung diseases, lung cancer, pulmonary infections and pleural disease.
Through the years, I have had employees complain of skin, eye, nose and throat irritation from wood dusts. Employees may also experience shortness of breath, dryness and sore throat, conjunctivitis (inflammation of the mucous membranes of the eye), and rhinitis (runny nose) when exposed to wood dust. Prolonged exposures can lead to the chronic health issues listed in the previous paragraph.
Fire and Explosion Hazards from Combustible Dust
Combustible dust is defined as a solid material composed of distinct particles or pieces, regardless of size, shape, or chemical composition, which presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations.
Dust explosions are a frequent hazard in underground coal mines, grain elevators, and other industrial environments. Many materials that would otherwise be considered safe, become dangerous when ground, cut, or shaved into small particles that become airborne. A spark, flame, or electrical arc is all these particles need to ignite and burn rapidly in the air.
Many common materials which are known to burn can generate a dust explosion, such as coal and sawdust. In addition, many otherwise mundane organic materials, thought to be stable, can become dangerous materials when in a fine dust and airborne. This would include: grains, hay, fertilizer, flour, starch, sugar, powdered milk, cocoa, coffee, and even aluminum, magnesium, and titanium when in fine particles.
When the concentration of a substance is at or below 25% of the Lower Explosion Limit (LEL) it is considered safe. In other words, when a substance is below the LEL, there is insufficient dust to support the combustion at the rate required for an explosion. When the fuel to air ratio of a substance increases above the upper explosive limit (UEL), there is insufficient oxidant to permit continuous combustion.
Determining the minimum explosive concentration or maximum explosive concentration of dusts in air is difficult. Typical explosive ranges in the air are from a few dozen grams/m3 for the minimum limit, to a few kg/m3 for the maximum limit.
For example, the LEL for sawdust has been determined to be between 40 and 50 grams/m3. There are many factors at play when calculating the component’s explosive ranges. The biggest factors are the ingredients of the component, concentration, size of the particles, humidity, and temperature. Under the right conditions, materials that are normally non-combustible can become explosive.
Therefore, any workplace activity that creates dust should be investigated to see if there is a risk associated with combustible dust. Employers need to be aware that dust can collect on surfaces such as rafters, roofs, suspended ceilings, ducts, crevices, dust collectors, and other equipment. In this case just because it is out of sight doesn’t mean that the danger has been reduced. When the dust is disturbed and becomes airborne under certain circumstances, there is a potential for a serious explosion.
Combustible Dust National Emphasis Program
In March of 2008, the U.S. Department of Labor, through the Occupational Safety and Health Administration (OSHA), initiated the Combustible Dust National Emphasis Program to address the hazards of dusts. The Combustible Dust National Emphasis Program referenced 1/32 inch dust accumulation levels as being the maximum accumulation allowed. This measurement is no longer the determining factor. The program was revised in March 26, 2012, with OSHA’s Hazard Communication Standard, and minor changes were made to this directive on October 1, 2015. This accumulation thickness is based on certain assumptions, including uniformity of the dust layer covering the surfaces and a bulk density of 75 lb./ ft3 of the material.
The National Fire Protection Association (NFPA)
NFPA 654 (2013) regulation allows the dust accumulation level to exceed the layer depth criteria of 1/32 inch in some circumstances. This depends on the layer depth (LD) and bulk density (BD) of the dust.
According to section 6.1.3.21 of NFPA 654 (2013 edition), a dust explosion hazard and dust flash fire hazard are deemed to exist in any building or room where any of the following conditions exists:
• The total area of nonseparated dust accumulations exceeding the layer depth (LD) criterion is greater than five percent of the footprint area.
• The area of any single nonseparated dust accumulation exceeding the layer depth (LD) criterion is greater than 1000 ft2.
• The total volume of nonseparated dust accumulations is greater than the layer depth (LD) criterion multiplied by five percent of the footprint area.
• The total volume of any single nonseparated dust accumulation is greater than the layer depth (LD) criterion multiplied by 1000 ft2.
• Bulk densities of combustible dusts depend on many factors including the type of material (e.g. wood, paper, plastic, metal, etc.), the dust particle size, and the dust particle shape.
The calculations to determine the maximum accumulation levels is more, than just a little complicated. The Combustible Dust National Emphasis Program directive CPL 03-00-008 is 43 pages in length. There are three OSHA Standards with regard to dust and dust accumulation 1910.22(a)(1), 1910.22(a)(2), and 1910.176(c) in which OSHA Compliance Officers reference for citations.
Addressing the Hazard through the Hierarchy of Control
Many employers make the mistake of using personal protective equipment (PPE) as their primary tool, or action in addressing the hazardous exposure that the employees are facing. Remember, PPE is the last defense in hazard controls. PPE may reduce the exposure to the health hazard to some extent, but it does nothing in the actual elimination of the physical hazard in the case of dust. Therefore the health hazard is always present, and the exposure itself is only being reduced, and not controlled, or eliminated. When the employee fails to wear the PPE, he or she is exposed to the health hazard. When it comes to the fire and explosion hazard related to dust, PPE has zero effect in controlling the physical hazard. Following the Hierarchy of Control for the control of hazards, is the proper sequence. As you can see in the pyramid, PPE is the least effective.
Hierarchy of Control Elimination
Can the health and physical hazards of the dust be eliminated? The equipment or process of cutting, sawing, sanding, or molding is a required task in the process, so most likely cannot be eliminated.
Substitution
Can the process or task be substituted for a safer equipment, process, or chemical? When it comes to dust, most likely not, since the process that creates the dust cannot be changed.
Engineering controls
Can engineering controls be put into place that will eliminate or control the hazard? When it comes to dust, there are many collection and vacuum systems available that are very effective in dust control. Will they eliminate the hazard completely? Maybe not, but they can reduce it to the point that the health hazard can be nearly, if not completely eliminated. To which point where PPE can be used to fully protect the employee from the remaining exposures. The physical hazard of fire and explosion can be controlled by taking the dust out of the environment in which the employees work.
Administrative controls
Administrative controls alone cannot control the health and physical hazard exposures of dust. Administrative controls can be utilized through operational policies, and the maintenance of the dust vacuum or collection system. Administrative controls will also be needed in employee training.
Personal protective equipment
PPE can be utilized to fully protect the employees in the work environment after the health hazards have been controlled. When the health hazard is eliminated, the use of PPE may not even be necessary. Again, PPE would have zero control of a fire and or explosion hazard, if it were present.
OSHA Consultative Services
I would highly recommend requesting OSHA Consultative Services, where available, for determining the health exposure hazards, and the fire and explosion hazards of dust. This service is free. Employers that use this service can find out about potential hazards at their worksites, improve their safety and health programs, and in most cases qualify for a twelve month exemption from routine OSHA inspections. Employers are not exempt from inspections due to serious accidents, or reported violations from employees.
These consultations are completely confidential, and the consultants cannot share their findings with the enforcement division, unless there are serious, life threatening situations that are not addressed. Consultation will not issue citations or penalties; they will provide you with a detailed list of non-compliances, in which you will have recommendations, and a grace period to resolve them. Any serious violations, that are considered life threatening, will require immediate correction.
OSHA Consultation Services has a wide range of testing equipment and test labs at their disposal, equipment and test labs that would otherwise be quite costly. For those that feel uneasy about having an OSHA consultation, a phone call to request information from them is free, and may ease your concerns of requesting them to visit your workplace.
Editor’s Note: Jary Winstead is a safety consultant, author and trainer who serves a variety of industries including the forest products sector. He owns Work Safety Services LLC and can be reached at SAFEJARY@gmail.com.
