Dangers of Combustible Dust by Dr. Paul Holdstock, Texene LLC.
The dangers of combustible dusts have been recognised for many years. Indeed there are long established standards issued by the National Fire Protection Association (NFPA), the Occupational Safety & Health Administration (OSHA) and other national and international bodies that address the issue. However, to date, these standards have in the main been voluntary. Whenever the standards have been implemented, it is clear that dust explosions have been reduced or eliminated, but it is also clear that implementation is not universal. Following three fatal dust explosions in 2003 alone that caused 14 deaths, the US Chemical Safety & Hazard Investigation Board (CSB) launched a wide ranging study of industrial dust explosions. They found that in the period 1980 to 2005 there were 281 dust fires and explosions in US businesses that caused the deaths of 119 people and injured 718 more. A quarter of the explosions occurred at food industry facilities, including sugar plants. Since the study was undertaken there have been a further 70 dust fires and explosions in the US.
The devastating fires and explosions that ripped through the Imperial Sugar refinery in Port Wentworth, GA. on February 7th, killing 13 workers and injuring many more, once again highlighted the dangers created by combustible dust. Sugar is only one of many common materials that can form combustible dusts. Others include flour, feed, plastics, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, and metals, etc. Many powders stored and transported in bulk bags can form combustible dust clouds when bags are filled or discharged. Powders are normally quite stable in bulk form, but when dispersed as a cloud, or when allowed to build up as a thin layer on surfaces, the combination of the powder and air can form an explosive mixture. All that is then required for an explosion to occur is an ignition source, which could be a naked flame, heating element, frictional spark or an electrostatic discharge.
On February 14th, 2013 the “Worker Protection Against Combustible Dust Explosions and Fires Act of 2013” was introduced in Congress. This Act mandates an interim standard for the regulation of combustible dusts to be issued, and followed by a final standard. The Act defines six essential requirements for the interim standard:
1) a hazard assessment to identify, evaluate, and control combustible dust hazards;
2) a written program that includes provisions for hazardous dust inspection, testing, hot work, ignition control, and housekeeping;
3) engineering controls, administrative controls, and operating procedures;
4) workplace inspection and housekeeping to prevent accumulation of combustible dust in places of employment in depths that can present explosion, deflagration, or other fire hazards, including safe methods of dust removal;
5) participation of employees and their representatives in hazard assessment, development of and compliance with the written program, incident investigation, and other elements of hazard management; and
6) providing safety and health information and annual training to managers and employees and their representatives.
The standard mandated by the new Act will place a legal responsibility on businesses to comply with its requirements, some of which will be effective within 30 days of publication of the interim standard. The requirements necessary to eliminate or mitigate hazards created by combustible dusts are already contained in codes and standards issued by NFPA, and it is likely that these will be implemented as part of the interim and final standard. The principal combustible dust control document is “NFPA 654, Standard for the Prevention of Fires and Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids”. NFPA also has commodity-specific combustible dust control standards, including NFPA 61 for agricultural and food processing facilities.
The requirements defined in the new Act echo the main components of the Explosive Atmospheres (ATEX) Directives in Europe. Directive 1999/92/EC, also known as ATEX 137, places a legal responsibility on employers to:
1) Eliminate explosive atmospheres whenever possible;
2) Identify and classify explosive atmospheres that cannot be eliminated;
3) Eliminate all possible ignition sources in areas classified as containing explosive atmospheres; and
4) Implement measures to mitigate any explosion that may occur.
Filling and Discharge Exposure
It is now incumbent upon all companies in the US and Europe to implement effective measures to prevent dust fires and explosions. In some situations, dust clouds are an inevitable part of a process. In such cases, the emphasis is very much on eliminating all possible ignition sources.
Dust clouds are inevitable when filling or emptying FIBC. The dust cloud may be confined to the space inside the bag or may extend outside the bag. Even with pellets and granular materials, dust clouds can be formed from the fines produced when conveying such material. Measures can be taken to mitigate the formation of dust clouds, such as slowing down the filling or emptying process, but as a precaution it is sensible to assume that some fine particulates will be airborne. In order to prevent the explosion of a dust cloud formed from combustible material, it is then necessary to eliminate all possible ignition sources from the areas in which dust clouds are formed, that is within the bag and in the immediate vicinity surrounding the bag. Most ignition sources such as naked flames, heating elements, etc. are easy to identify and eliminate from FIBC handling areas. However, there is one ignition source that may not be quite so obvious but is none the less just as dangerous and requires careful consideration: static electricity.
Static Electricity, are you at Risk?
Static electricity is the ignition source in about 13% of all chemical fires and explosions (Source: Marc Rothschild – Rohm and Haas). Static electricity is generated whenever materials come into contact and rub against each other, particularly when the materials are in particulate form and being moved at significant speeds. Electrostatic charge will readily accumulate on plastics and other insulating materials, which may ultimately result in a spark or brush discharge capable of igniting a flammable atmosphere. In the absence of any measures to control static electricity, there is a real risk that filling or emptying an FIBC will generate enough static electricity to cause and incendiary discharge.
Solutions for Flexible Packaging
There are FIBCs available that do incorporate measures to control static electricity. The US Standard NFPA 654 and the European Code of Practice CLC/TR 50404 permit the use of Type C or Type D FIBC when handling very sensitive combustible powders or where flammable gases or vapours may be present. Type C and Type D FIBC are made like most FIBC from woven polypropylene fabric, but they contain components designed to dissipate static electricity. Type C FIBC contain an interconnected network of conducting yarns that must be grounded in order to dissipate static electricity safely. The need for grounding is the major weakness of Type C. In a detailed investigation of explosion incidents involving FIBC, Dr. Lawrence G. Britton discussed the dangers of using ungrounded Type C FIBC and stated “In particular it should be appreciated that the potential for operator grounding error and sudden nemesis can be very high”. The correct use of Type C FIBC will eliminate static electricity as a potential ignition source, but it will require significant capital investment in appropriate fail-safe grounding systems and on-going costs to maintain equipment and train operators. And there is still the risk of human error.
CROHMIQ® Static Protective Type D FIBC
A simpler and better solution to the problem of controlling static electricity is available. CROHMIQ® Static Protective Type D FIBC were the first to provide full control over static electricity without the need for grounding. CROHMIQ® FIBC safely dissipate electrostatic charge safely into the atmosphere via low energy corona discharging. The components used to dissipate charge are an integral part of the woven polypropylene fabric used to construct the FIBC. There is no need to ground CROHMIQ® FIBC and so the need for complex and expensive grounding systems is eliminated, as is the risk of human error. CROHMIQ® FIBC are intrinsically safe and require no input from operators when filling or when emptying.
CROHMIQ® FIBC are designed and engineered to provide total electrostatic safety across a wide range of industries without the need for grounding. This unique static protective technology was pioneered by CROHMIQ’s engineers in 1995. Since then, CROHMIQ® FIBC have been used to package over 50 billion pounds of products for the world’s most demanding industries, including pharmaceuticals, fine chemicals, pigments, and food products. CROHMIQ® FIBC comply with FDA and EU regulations for food contact applications and meet all the essential safety requirements of national and international standards including IEC 61340-4-4 Ed. 2.0, NFPA 654 and CLC/TR 50404.
CROHMIQ® FIBC are used throughout the world by major companies as an essential part of their regulation of combustible dust hazards. Thanks to their outstanding 15-25-50 Safety Record, CROHMIQ® FIBC are widely acknowledged as the safest and most cost effective solution for controlling static electricity in FIBC handling operations.
For more information about CROHMIQ® FIBC fabrics, visit www.crohmiq.com
Acts of Congress and European Commission Directives
H.R. 691 – Worker Protection Against Combustible Dust Explosions and Fires Act of 2013.
Directive 1999/92/EC – Minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres (ATEX 137).
Testimony of the Honorable William E. Wright, Board Member and Interim Executive U.S. Chemical Safety Board Before the U.S. House of Representatives Committee on Education and Labor, March 12, 2008.
Testimony for the House Education and Labor Committee on H.R. 5522,The Combustible Dust Explosion and Fire Prevention Act of 2008 by Amy Beasley Spencer, Senior Chemical Engineer, National Fire Protection Association, March 12, 2008.
NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities.
NFPA 484, Standard for Combustible Metals.
NFPA 654, Standard for the Prevention of Fires and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.
NFPA 655, Standard for Prevention of Sulfur Fires and Explosions.
NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities.
IEC 61340-4-4 Ed. 2.0, Electrostatics – Part 4-4: Standard test methods for specific applications – Electrostatic classification of flexible intermediate bulk containers (FIBC).
CLC/TR 50404, Electrostatics – Code of practice for the avoidance of hazards due to static electricity.