One of the most common questions we get about combustible dust is whether an industrial vacuum is really necessary. Won’t a shop-style vacuum do the trick?
While shop-style vacuums (i.e., the kind you’ll find at The Home Depot or Lowe’s) are great for cleaning your garage, your home woodworking shop, and even some commercial applications, they aren’t recommended for industrial applications. This is because they frequently create sparks. If combustible dust is present, using these vacuums can create a significant explosion hazard.
What NFPA 652 says about vacuum cleaners
Combustible dust is a major problem in manufacturing and industrial processing facilities. It causes fires and explosions every single day. Fortunately, most of them are contained before they become big enough to make the news. But every wayward spark in a processing plant has the potential to cause an explosion if it comes into contact with the right dust cloud.
To help processors understand this hazard and prevent incidents, the National Fire Protection Association (NFPA) issued NFPA 652: Standard on the Fundamentals of Combustible Dust. This standard identifies specific design requirements for portable vacuums used in all facilities that manufacture, process, blend, convey, repackage, generate, or handle combustible dusts, even if those facilities aren’t classified as hazardous locations.
These requirements include:
- Vacuums must be constructed from conductive materials.
- Hoses must be conductive or static dissipative.
- All conductive components must be bonded and grounded.
- Dust-laden air must not pass through the fan or blower.
- And more — view the full list here.
Most shop-style vacuums don’t meet all of these requirements. And because they don’t meet these requirements, they can pose an explosion risk.
Let’s look at the properties of many shop-style vacuums that make them not just insufficient, but dangerous, for combustible dust applications.
Insulative, rather than conductive, materials
The first few design requirements in NFPA 652 specify that vacuums and their hoses must be constructed using conductive or dissipative materials. These terms refer to how easily an electric charge flows across the surface of the materials. Both conductive and dissipative materials allow electricity to flow easily to ground.
Insulative materials, on the other hand, do not allow an electric charge to flow to ground. Instead, the charge builds up over time, and when it discharges, sparks can fly.
True industrial vacuum cleaners are built using stainless steel or other conductive materials that are electrostatic discharge safe. Most shop-style vacuums are not. They often have bodies made of plastic and hoses made of rubber — both of these materials are insulative. In addition, most shop-style vacuums have a small cartridge filter that is not antistatic. All of these components contribute to an explosion risk.
NFPA 652 also requires that all conductive components be bonded and grounded. This is because if a charged, ungrounded object comes into contact with a grounded object, it can cause a spark or an electric arc. If that spark or arc reaches a combustible dust cloud, it can put an entire facility at risk.
All conductive components on industrial vacuum cleaners are bonded and grounded. With a shop-style vacuum cleaner, this may not be the case.
A cautionary tale
“Using a shop vac to minimize dust may sound like a good idea, but I’ll stick with an explosion-proof dust collection system–like those used for woodworking. We used to use a shop vac to clean the milling room, until one of our employees got (quite literally) knocked on her butt by a static electric discharge from the grain passing through the plastic hose. Now every bit of plastic the grain passes through (drop tubes, dust collection hoses) in our mill house has a grounding wire inside, even if the run is only a foot or less.”
Another problem some shop-style vacuum users report is the motor sparking. This can happen even with brand new machines, and typically will get worse over time as the motor brushes wear out.
As we mentioned before, where combustible dust is present, any spark could be the one that sets off a catastrophic event. A vacuum cleaner whose motor sparks every time you use it presents too many opportunities for such an event to occur.
Shocking the operator
Finally, if you read the online forums for communities where shop-style vacuums are used, like woodworking and homebuilding, you’ll quickly encounter another problem commonly reported for shop-style vacuums: they shock the operator.
This leads to risk in a couple of ways. First, the shock itself is a spark, which can cause an explosion. But also, getting shocked is annoying and painful, and it can disincentivize people to use the vacuum to perform thorough housekeeping. If you decide not to clean your backyard workshop for a couple of days, you’ll end up with a messy workshop. If you decide not to clean your processing facility, you could end up with a hazardous level of dust accumulation.
Shop-style vacuums simply weren’t made for the demands of collecting combustible dust in a manufacturing or industrial processing facility. Using them can be dangerous to your plant and your workers.
It can also result in penalties. For example, in 2010, OSHA fined a pellet mill $30,000 for violations including “the use of an unapproved spark-producing shop vacuum in a Class II, Division 2 location, and not training employees on specific work procedures to protect themselves from the explosive properties of wood dust.”