Combustible Dust Hazard Analysis and Testing

Combustible dust is dangerous. In the last decade dust has caused dozens of explosions across the country which have destroyed facilities and injured or killed hundreds of people. A pivotal example of this was the dust explosion which occurred in a Georgia sugar plant, killing 13 and seriously injuring 60. You can watch a video about this incident at the bottom on this page.

Following this tragedy, the U.S. Department of Labor Occupational Safety & Health Administration (OSHA) began a more rigorous initiative, called the National Emphasis Program (NEP), to make sure plants across all industries took the risks associated with combustible dust seriously.

 

The U.S. Congress required OSHA to enforce National Fire Prevention Association (NFPA) 654 Standard. These standards are the basis for OSHA’s housekeeping regulations and its Combustible Dust National Emphasis Program and Failure to comply can mean fines (See OSHA Directive No. CPL 03-00-008.)

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July 24, 2017

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Does this affect me?

The U.S. Congress required OSHA to enforce National Fire Prevention Association (NFPA) 654 Standard. These standards are the basis for OSHA’s housekeeping regulations and its Combustible Dust National Emphasis Program and Failure to comply can mean fines (See OSHA Directive No. CPL 03-00-008.)

See OSHA Directive No. CPL 03-00-008.
If your facility contains the following types of dust you must pay attention:
  • Metal dust such as aluminum and magnesium.
  • Wood dust
  • Coal and other carbon dusts
  • Plastic dust and additives
  • Biosolids
  • Certain textile materials
  • Other organic dust such as sugar, flour, paper, soap, and even dried blood.
In addition the OSHA NEP is aimed at specific industry groups that have experienced either frequent combustible dust incidents or combustible dust incidents with catastrophic consequences.
The industries included are:
  • Agriculture
  • Food Products
  • Chemicals
  • Textiles
  • Forest and furniture products
  • Metal processing
  • Tire and rubber manufacturing plants
  • Paper products
  • Pharmaceuticals
  • Wastewater treatment
  • Recycling operations
  • Some coal handling and processing facilities

NFPA 654 Code

The most recent version of NFPA 654 requires facilities to take a more performance-based approach to understanding and managing these dust hazards. This standard is very similar to OSHA's earlier Process Safety Management standard and contains many of the same requirements. A few of the similar requirements are process hazard analysis, management of change, training, hot work and mechanical integrity.

Stringent compliance levels:

According to NFPA 654, “Dust layers 1/32 inch (0.8 millimeters) thick can be sufficient to warrant immediate cleaning of the area.” FYI, this is about the diameter of a paper clip wire or the thickness of the lead in a mechanical pencil!

The standard continues to say that “the dust layer is capable of creating a hazardous condition if it exceeds 5 percent of the building floor area. This means if your floor area is 20,000 square feet, a 1,000-square-foot layer of dust throughout the facility would be the upper limit. The practical reality is that there is a zero-tolerance approach to combustible dust buildup in plants.

Critical questions you must answer:

There are three questions that must be answered before practical solutions for dust management can be determined.
  1. What is the risk potential for my workplace?
  2. What are the tolerance levels for the type of dust I have?
  3. What can be done to best protect employees and assure compliance with regulations?
Let’s take a closer look at the answers to each of these questions.

#1-What is the risk potential for my workplace?

This is the first question that must be answered to understand the hazard at your facility. Safety Links will conduct an initial walk-through along with an evaluation of any existing dust control systems. The walk-through focuses on dust containment practices, design of equipment safeguards (e.g., isolation), existence of explosion protection, grounding and bonding and appropriate electrical classification.

The management systems evaluated will include those recommended by the NFPA 654 (Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids) including process hazard analysis, management of change, training and procedures, hot work, inspection and maintenance.

Afterwards a report will be issued with the results of the preliminary assessment, including key prescriptive safeguard requirements as recommended by applicable codes and standards including the NFPA 654 and OSHA’s guidance documents NEP, CPL 03-00-008.

Where a more comprehensive assessment of the actual dust is necessary (e.g., to meet the new NFPA 654 performance standard) or desired (e.g., where a high level of potentially combustible dust hazard exists), our Safety Professionals can help develop a dust sampling strategy. This strategy will help characterize the dust and provide objective data needed to answer the second question.

#2-What are the tolerance levels for the type of dust I have?

Each dust compound has unique physical and chemical characteristics. A good understanding of both is essential to understand the hazards, and ultimately the risks, associated with the dust being handled. Safety Links has assisted many organization’s with the development of a comprehensive testing plan appropriate for the handling operations being evaluated. By targeting their specific needs, overall testing costs are reduced and safety is improved.

To properly characterize most dusts, testing of an actual process sample is required. This ensures the measured data is representative of the dust present in the process being analyzed. Properly characterizing the dust hazard prevents unnecessary safeguards from being recommended, particularly if the overall risks do not justify the conservative designs many are incorporating.

Depending on the type of process being analyzed and the potential explosion prevention measures to be employed, a testing plan will be selected.

Dust Explosion Tests Available

All explosive Dust Samples taken by Safety Links are analyzed by Chilworth Laboratories an ISO/IEC 17025 Accredited Laboratory which is internationally recognized as the leader in explosive dust testing. Chilworth’s testing methods conform to the American Society for Testing and Materials (ASTM) Methods, National Fire Protection Association (NFPA) Standards, and other international standards including the International Standards Organization (ISO) Methods.

Explosibility Screening Test – Go / No Go Test

The explosibility screening test determines whether a powder or dust will explode when exposed to an ignition source when in the form of a dust cloud. The test results in a material being classified as either Type Go — explosible — or Type No Go — non-explosible. Thus, the test is also known as the Go / No Go Test.

Minimum Ignition Energy Test – Dust Cloud

The minimum ignition energy (MIE) test determines the lowest spark energy capable of igniting a sample when dispersed in the form of a dust cloud. The test is used primarily to assess the potential vulnerability of powders and dusts to electrostatic discharges, but is also relevant to frictional sparks.

Minimum Ignition Energy – Dust Layer

The minimum ignition energy (MIE) of a dust layer is determined by placing a dust layer sample on a ground metal plate and approaching the surface of the sample from above using a spherical electrode. The electrode is connected to a capacitor bank and high voltage power source and is capable of delivering electrostatic discharges of known energy to the powder sample. Trials are performed for varying discharge energies and layer depths until the MIE of the dust layer sample has been determined.

Minimum Ignition Temperature Test – Dust Cloud

The minimum ignition temperature (MIT) test determines the lowest surface temperature capable of igniting a powder or dust dispersed in the form of a dust cloud. The MIT is an important factor in evaluating the ignition sensitivity of powders and dusts and is relevant for defining the maximum operating temperature for electrical and mechanical equipment used in dusty environments.

Minimum Ignition Temperature Test – Dust Layer

The MIT-Layer test determines the lowest surface temperature capable of igniting a powder or dust when in the form of a five (5) millimeter (mm) or 12.7 millimeter (mm) (other depths may be used) layer. The MIT of a dust layer is used together with the MIT of a dust cloud to define the maximum operating temperature for electrical and mechanical equipment used in dusty environments.

Minimum Explosible Concentration Test

The minimum explosible concentration (MEC) test determines the smallest concentration of material in air that can give rise to flame propagation upon ignition when in the form of a dust cloud. The test involves dispersing powder or dust samples in a vessel and attempting to ignite the resulting dust cloud with an energetic ignition source. Trials are repeated for decreasing sample sizes until the MEC is determined.

Limiting Oxygen Concentration Test

The limiting oxygen concentration (LOC) determines the minimum concentration of oxygen (displaced by nitrogen) capable of supporting combustion. An atmosphere having an oxygen concentration below the LOC is not capable of supporting combustion and thus cannot support a dust explosion. The LOC test is used to study explosion prevention or severity reduction involving the use of inert gases and to set oxygen concentration alarms or interlocks in inerted plant and vessels.

Explosion Severity Test (Maximum Explosion Pressure, Kst)

A powder or dust sample is dispersed within the sphere, ignited by chemical igniters, and the pressure of the resulting explosion is measured. The sample size is varied to determine the optimal dust cloud concentration. The maximum pressure and rate of pressure rise are measured and used to determine the Kst value and St hazard class of the material. These data can be used for the purpose of designing dust explosion protection measures and equipment.

3-What can be done to best protect employees and assure compliance with regulations?

The third and final question is best answered by eliminating the potential for dust concentrations to build up.
  • Minimize the escape of dust from process equipment or ventilation systems
  • Use dust collection systems and filters
  • Utilize surfaces that minimize dust accumulation and facilitate cleaning
  • Provide access to all hidden areas to permit inspection
  • Inspect for dust residues in open and hidden areas, at regular intervals
  • Clean dust residues at regular intervals
  • Use cleaning methods that do not generate dust clouds, if ignition sources are present
  • Only use vacuum cleaners approved for dust collection
  • Locate relief valves away from dust hazard areas; and
  • Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in writing with established frequency and methods)

If the dust cannot be controlled at the source another option is to control ignition sources.

  • Use appropriate electrical equipment and wiring methods
  • Control static electricity, including bonding of equipment to ground
  • Control smoking, open flames, and sparks
  • Control mechanical sparks and friction
  • Use separator devices to remove foreign materials capable of igniting combustibles from process materials
  • Separate heated surfaces from dusts
  • Separate heating systems from dusts
  • Proper use and type of industrial trucks
  • Proper use of cartridge activated tools
  • Adequately maintain all the above equipment

The use of proper electrical equipment in hazardous locations is crucial to eliminating a common ignition source. Once these areas have been identified, special Class II wiring methods and equipment (such as "dust ignition-proof" and "dust-tight") must be used as required by 29 CFR 1910.307 and as detailed in NFPA 70 Article 500. It is important not to confuse Class II equipment with Class I explosion-proof equipment, as Class II addresses dust hazards, while Class I addresses gas, vapor and liquid hazards. The use of industrial trucks is regulated by OSHA’s Powered Industrial Trucks standard (29 CFR 1910.178). Hazardous atmospheres including dust concentrations are addressed in paragraph (c) of this standard.
The final option is Damage Control.

  • Separation of the hazard (isolate with distance)
  • Segregation of the hazard (isolate with a barrier)
  • Deflagration venting of a building, room, or area
  • Pressure relief venting for equipment
  • Provision of spark/ember detection and extinguishing systems
  • Explosion protection systems (also refer to NFPA 69, Standard on Explosion Prevention Systems)
  • Sprinkler systems
  • The use of other specialized suppression systems

Related Standards and more information

  • NFPA Guidelines: NFPA 68. Venting of Deflagrations, NFPA 77. Recommended Practice on Static Electricity, NFPA 654. Prevention of Fire and Dust Explosions, NFPA 704. Annex E Instability, Thermal Hazard Evaluation Techniques (NFPA Link- http://www.nfpa.org/catalog/)
  • OSHA Standards: 1910.119 Process Safety Management of Highly Hazardous Chemicals National Emphasis Program on Combustible Dusts (2007)
CLICK TO CONTACT US
July 24, 2017

CONTACT SAFETY LINKS

Below you will find our various contact information, we look forward to hearing from you.

Office Hours
Mon - Fr 7:00am - 4:00pm

Phone
Toll Free: 1-800-768-7036
Office: 407-545-4699

Email
info@safetylinks.net

CLICK HERE TO GO TO OUR FULL CONTACT PAGE

SAFETY LINKS

© IOA Safety 2003-2015
4602 35th Street, Suite 400. Orlando, FL 32811.

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