Preventing a Disaster

A Tutorial on Explosion Proof Vacuums

Author: Paul Miller,
Vice President & General Manager of Nilfisk CFM

In February of 2008, a sugar plant near Savannah, Georgia suffered the ultimate tragedy. Fourteen employees were killed and 40 injured when finely ground motes of sugar dust ignited, setting off a violent blast. If the fatalities and a tarnished reputation weren’t enough, the Department of Labor’s Occupational Safety and Health Administration (OSHA) then fined the company more than 8 million dollars in workplace violations related to combustible dust.

Although it took a fatal accident in a sugar plant to make combustible dust a national headline, industrial facilities have been aware of the risk for years. While the U.S. Chemical and Safety Hazard board estimates there are on average 10 explosions, 5 fatalities, and 29 injuries per year as a result of combustible dust-related incidentsi, the reality is that these numbers are most likely underestimates, especially since smaller incidents such as fires and blasts without injuries happen daily and often go unreportedii

So what can be done to prevent these types of accidents in the future? In March 2008, OSHA reissued their National Emphasis Program (NEP) on combustible dust to call attention to the agency’s rigorous expectations for combustible dust-related explosion prevention, which includes random unannounced audits.iii The program also outlines recommendations for decreasing plants’ risk of an explosion and includes incorporating an industrial vacuum into maintenance plans as a means to eliminate potentially hazardous dust that settles on overhead pipes, walls, floors and machinery of industrial facilities.



 

Certifiable Explosion-Proof: Beware of “Dress Up”

Purchasing an industrial vacuum to combat combustible dust sounds easy enough, but there is actually some complexity to the investment, especially if the vacuum will be used to collect classified hazardous materials like coal, fuel, or even sugar. Naturally, most plant supervisors assume the machinery in their plants is explosion-proof, including the industrial vacuums, but if you plan on collecting hazardous materials, a certified “explosion-proof” vacuum (EXP) is imperative. In fact, using just a basic vacuum, made of metal parts and exposed motors, can actually add to the risk of explosion.

An EXP is explosion-proof to the core. This means that everything from the outer shell to the internal mechanics including the motor, switches, filters and inner chambers are grounded and constructed of non-sparking materials like stainless steel. Some industrial vacuum companies offer basic models dressed up with a few anti-static accessories and describe them as suitable for explosive material. These imposters can still create arcs, sparks or heat that can cause ignition of the exterior atmosphere and overheating that can ignite dust blanketing the vacuum.

Purchasing an explosion-proof vacuum approved by a nationally recognized testing agency such as the Canadian Safety Association (CSA) or Underwriters Laboratories (UL) will protect buyers from purchasing a poser by providing legal certification that the vacuum can be used in a particular NFPA-classified environment. It ensures every component in the vacuum from the ground up meets strict standards for preventing shock and fire hazards.

Explosion-Proof Vs. Intrinsically Safe

In environments where electricity is unavailable or undesirable, air-operated vacuums for hazardous locations are excellent alternatives. It is important to note that only electric vacuums can be certified and deemed “explosion-proof,” but properly outfitted pneumatic vacuums, referred to as “intrinsically-safe,” can pack the same punch as their electric counterparts while still meeting the requirements for use in NFPA-classified environments. Plant managers should beware of vacuum companies that refer to their



 

pneumatic models as “certified explosion-proof.” Explosion-proof certification for air-operated machines simply does not exist.

Filtration

Superior filtration does not have to be sacrificed on an explosion-proof model, especially when collecting potentially hazardous materials. For peak safety and operating efficiency, an EXP vacuum should have a multi-stage, graduated filtration system, which uses a series of progressively finer anti-static filters to trap and retain particles as they move through the vacuum. In order to eliminate combustible dust from being exhausted back into the ambient air, a HEPA or ULPA filter can be positioned after the motor to filter the exhaust stream. Quality HEPA filters offer an efficient, effective way to trap and retain the smallest dust particles, down to and including 0.3 microns. An ULPA filter captures even smaller particles, down to and including 0.12 microns.

Liquid Spill Response

Spill response should also be taken into account when purchasing an explosion-proof vacuum. Although OSHA’s National Emphasis Program is specifically looking at companies that handle dry solids, manufacturers’ maintenance plans are also under the microscope. If workers might need to collect flammable or explosive chemicals, a wet-model explosion-proof vacuum should be considered, also available in both electric and air-operated versions.

Conclusion

On April 29, 2009, OSHA announced that they are initiating a comprehensive rulemaking on combustible dust. In the coming months, the agency will issue an Advanced Notice of Proposed Rulemaking and convene related stakeholder meetings to evaluate possible regulatory methods, and request data and comments on issues related to combustible dust such as hazard recognition, assessment, communication, defining combustible dust and other concerns.iv The use of industrial vacuums, specifically explosion-proof models, as a preventative method will most likely be a part of those discussions, and ultimately appear in the final OSHA standard.



 

Purchasing a high-quality certified explosion-proof or intrinsically-safe vacuum is a solid first step in preventing a combustible-dust related explosion, and picking the right vacuum often raises a lot of questions, especially when it comes to disaster prevention. Like all investments, pre-sale research is key. Plant managers shouldn’t hesitate to ask the vacuum-manufacturer for an onsite analysis of their vacuum needs in order to recommend what type of vacuum, hose and accessories are needed for the application. With the right equipment, the vacuum can be used to collect dust and debris from the floor, machinery, walls, and even overhead pipes and vents. And naturally, every manufacturer will be responsive to your needs before you buy, so look for a company that will still be there after the bill is paid. Excellent post-sale support and training will make things easier when it’s time to purchase replacement parts and filters or service the vacuum.

If used consistently and in conjunction with a comprehensive maintenance plan, the facility’s investment in an explosion-proof vacuum will result in much more than just a clean plant; It will save money, protect company integrity, increase productivity, and most importantly, protect the most valuable asset, employees.

SIDEBAR

An ignitable material, an ignition source and oxygen- all it takes for a potential explosion at your facility. Most manufacturing plants have all three. In 2006, fatalities involving explosions and fires increased by 26% in the manufacturing sector according to the Bureau of Labor Statistics Census of Fatal Occupational Injuries. In addition to injuries, explosions cost companies millions of dollars. Between 1992 and 2002, Factory Mutual Global’s pharmaceutical and chemical clients experienced dust explosions resulting in $32 million in losses. And OSHA has estimated that there are approximately 30,000 U.S. facilities at risk for combustible dust explosions. Simply put, there’s a lot of stake.

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, contains



 

comprehensive guidance on the control of dusts to prevent explosions. The following are some of its recommendations:

           
– 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).

 

i “Investigation
Report: Combustible Dust Hazard Study”. U.S. Chemical Safety and Hazard
Investigation Board. 02 Jan 2008. <http://www.csb.gov/completed_investigations/docs/Dust%20Final%20Report%20Website%2011-17-06.pdf>

ii “OSHA Combustible Dust Prerule Agenda.” Combustible
Dust Policy Institute. 03 Jun 2009. http://www.combustibledust.com

iii “Combustible Dust National Emphasis Program”.
Occupational Health and Safety Association. 02 Jan 2008. <http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=3729>

iv “U.S. Department of Labor’s OSHA announces rulemaking
on combustible dust hazards.” National News Release. Occupational Health and
Safety Association. 03 Jun 2009. http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=NEWS_RELEASES&p_id=17828