Sometimes it’s necessary to cut or weld, or hot work in the vicinity of your dust collector. However, this can be extremely dangerous if your dust is explosive. A dust collector, after all, is an accumulation of dust. If that material is combustible, careless hot work could lead to a catastrophic explosion.
“Hot work” is defined by OSHA as “welding, brazing, cutting, soldering, thawing pipes, using heat guns, torch applied roofing and chipping operations, or the use of spark-producing power tools, such as drilling or grinding”. Most of us would think twice about welding or cutting in near a dust collector or any other combustible dust. But some tools, even ones that shouldn’t produce sparks, may have faulty wiring. This can lead to a fire or explosion.
Hot Work Procedures
No hot work should be done near the dust collector without the correct procedures (see NFPA 51B). This NFPA standard specifically defines the procedures for conducting this type of work anywhere that it might cause an explosion.
Hot work near or on a dust collector might include repairs or adding/removing a piece of equipment or ductwork. It may include any number of other projects. Before doing this kind of work around the dust collector, you must have a hot work procedure IN WRITING:
- Shall be in writing and available to anyone conducting hot work in the area
- It must require an inspection of the work area before the work starts
- Must have a permit signed to show that all phases of the work have been inspected and approved
The program should assess safety equipment in the area. On a dust collector that might include a spark arrestor, spark detector, fire suppression or sprinkler system, abort gate, explosion venting, or other types of fire and explosion safety devices.
Hot work may require completely blocking the ductwork to the dust collector, or if the work is on or close to the collector, may require removing the filters, emptying or removing the hoppers, and thoroughly cleaning the entire dirty air side of the dust collector. a strong g recommendation is that a fire suppression system is in place before hot work begins. This will suppress any fire that might start. Further, remove as much of the dust as possible if it is explosively combustible.
Permits Ensure Safety
NFPA 51B specifies that the company safety specialist will issue a permit for work to proceed once achieving an inspection and determination of safety for hot work. It’s the job of this designated safety specialist to inspect the area of hazards. The specialist ensures the removal of all combustible dust. They confirm the isolation of all sparks and heat and establish safety procedures in the event of a fire.
No one should be allowed to perform ANY type of hot work, including the use of spark-producing power tools, in the vicinity of the dust collector without a permit. However, it happens all the time and puts lives at risk if the dust is combustible. Take the time to assess this hazard in your own workplace. If the hazard exists, your safety professional should set up hot work procedures to make sure no one puts themselves or the facility at risk.
In the agricultural industry, grain dust explosions are a hazard that must be addressed. According to a report from Purdue University, grain dust explosions have occurred at a constant rate over the last ten years, with little change in the number of explosions, injuries, and fatalities. They report an average of 9.3 explosions each year over the past decade.
Since OSHA instituted Standard 29 CFR in 1988, which specifically details safety in grain handling facilities, there has been a focus on the control of what OSHA refers to as “fugitive grain dust”. Preventing grain dust explosions was a focus, including regulations on any type of “hot work” occurring in the vicinity of grain dust. The standard requires testing for combustible dust presence in all storage containers (silos, tanks, bins). It also requires thorough housekeeping procedures to keep dust from accumulating on surfaces.
Grain dust collection systems are strongly recommended, and they must be designed to resist an explosion or deflagration. Correctly designed systems can prevent an explosion from happening or prevent it from causing damage or injury.
Purdue University’s report examines the number of grain dust explosions that occur each year. From 1995 to 1998 the number of explosions was high, reaching 18 grain dust explosions in 1998. Numbers stayed below the ten-year average until 2005, with 13 explosions, and then in 2008, with 19 explosions.
The most common months for grain dust explosions, according to the report, are April, August, and September. The report suggests that during these months, there is increased handling and moving of grain.
What’s causing these explosions? Some facilities think that they don’t need to worry about a little accumulated dust as long as there’s no ignition source. As our own Charlie Miller would say, “good luck with that”… in 67.8% of incidents, the ignition source was unknown. Only 6% could be related to fire, with less than 4% related to sparks or mechanical failures. Most of the time, nobody knows what triggered the explosion, which makes it very difficult to prevent an explosion when fugitive dust is present.
The high percentage of unknown ignition sources should be proof that the only prevention for grain dust explosion is to keep fugitive grain dust under control in all parts of the facility at all times. A dust collection system is essential to this, and can include a baghouse, a cartridge collector, or spot filters located at specific grain handling points.
Some other interesting statistics related to combustible dust explosions in the grain industry:
From 2007 to 2016, there were 91 dust explosions, and 52 of those were caused by corn dust. The second most hazardous type was mixed feed, which probably includes corn quite often, with 19 explosions. 20 explosions out of 91 were caused by other types of dust.
In 2017, there were 7 grain dust explosions, slightly below the ten-year average of 9. The locations included a pet food plant, a grain mill, and 5 grain elevators. Grain elevators move large quantities of grain and create a high risk of explosion.
In the last ten years, there have been 101 injuries and 15 fatalities due to grain dust explosions. 55 of the explosions occurred in grain elevators, with feed mills a distant second at 18.
If grain elevators are so hazardous, how can the risk be decreased? Spot filters are often a very good solution for dust control on these facilities. They can be placed almost anywhere that dust is generated and are self-cleaning, requiring only occasional maintenance. They do not require confined space permits to work in and can control fugitive grain at the source.