Haz-Loc PVCO’s Blog

Protecting Workers from Combustible Dust Explosion Hazards

In this new Fact Sheet OSHA reminds us combustible dusts shall be collected by using a “properly designed, installed, approved and maintained dust collection system.” Portable vacuum cleaners shall be NRTL certified and classified for the type of dust it will be used. For example: for the collection of metal dust (such as aluminum in an automobile repair shop) a vacuum cleaner shall be classified for Class II Group E.



Following three catastrophic dust explosions that killed 14 workers in 2003, the US Chemical Safety and Hazard Investigation Board (CSB) initiated a study of dust explosions in general industry and what can be done to reduce their risk. The CSB has concluded that combustible dust explosions are a serious hazard in American industry.

The CSB report reminds us that dust explosions can either be primary or secondary, and that a secondary explosion occurs when dust accumulated on floors or other surfaces is lofted and ignited by a primary explosion

The best way to prevent secondary dust explosions is to minimize dust accumulations. Ensuring good housekeeping can effectively prevent secondary dust explosions. However, proper equipment and techniques to clean combustible dust accumulations must be used. Care
must be taken to minimize dust clouds, and only vacuum cleaners approved for combustible dust locations used as mentioned in NFPA 654 (2013)

You can read the complete report at:

Good Housekeeping Program Controls Combustible Dust Hazards

“Housekeeping is often one of the first things that OSHA will consider during an inspection. Additionally, establishment of a proper housekeeping plan for a facility that produces fugitive dust is a requirement of NFPA 654, Chapter 8 – Fugitive Dust Control and Housekeeping.”


Combustible dusts shall be collected into an adequately designed collection system

Here is an example reported by OSHA where combustible particulate solids were not collected into an adequately designed dust collection system.

OSHA reminds us that “An effective dust collection system, proper industrial hygiene and frequent cleaning are critical to preventing a dangerous and potentially fatal buildup of combustible dust in the workplace.”

US Labor Department’s OSHA proposed $90,500 in fines against the concerned company for fire and explosion hazards.

See the OSHA citation for combustible dust fire and explosion hazards:


Choose the right vacuum cleaner for your application

Certified equipment surrounds us. The certification covers hazards in the specific environment where the equipment is used.

As far as vacuum cleaners are concerned the certification usually does not cover the hazards for the collection of certain type of dusts or liquids. In such case users must validate the application for which the equipment is designed before buying it. This is particularly important when a vacuum cleaner is used to collect combustible dusts or flammable liquids.

Combustible metals housekeeping as per NFPA 484 “Standard for combustible metals”

Cleanup procedures for fugitive dust accumulations (7.3)

First thing: “Fugitive dust shall not be allowed to accumulate to a level that obscures the color of the surface beneath it.” (7.3.1)

Second: “It shall be permissible to establish, in a building or room, an alternate housekeeping dust accumulation threshold based on a documented hazard assessment acceptable to the AHJ.” (7.3.2)

Third (concerning vacuum cleaning systems): “Periodic cleanup of fugitive dusts shall be accomplished by using…Dedicated vacuum cleaning systems designed for handling combustible metal powders” (7.3.3) and “portable vacuum cleaners shall be used only if listed for the material being vacuumed” (7.5.4)

In addition, and for the collection of combustible metals, it is important to choose an equipment which has been manufactured in compliance with the good manufacturing practices. Always refer to the operation manual to see the applications for which the vacuum cleaner has been designed for.

OSHA Dust Control Recommendations

OSHA Dust Control Recommendations:
• Implement a hazardous dust inspection, testing, housekeeping, and control program;
• Use proper dust collection systems and filters;
• Minimize the escape of dust from process equipment or ventilation systems;
• Use 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;
• If ignition sources are present, use cleaning methods that do not generate dust clouds;
• Use only vacuum cleaners approved for dust collection
• Locate relief valves away from dust deposits.

“Use proper dust collection systems and filter” : The equipment must be certified for use in the concerned hazardous location. Refer to the NRTL certificate of compliance.

“Use only vacuum cleaners approved for dust collection”: The vacuum cleaner must be designed to safely collect the concerned dust. Refer to the instruction manual.


Choosing a vacuum cleaner for use in hazardous locations

A regular and efficient housekeeping is recommended in hazardous locations to prevent hazards due to combustible and flammable materials buildup.

The use of an appropriate and safe equipment for this task is most important and should be part of the initial hazards analysis.

When it’s time to choose a vacuum cleaner two main aspects have to be considered:

1-is the equipment safe to be used in the hazardous location?
2-is it designed to safely collect the hazardous waste?

Regarding the first aspect you need to know the kind of hazardous location the vacuum cleaner will be used in and validate that the equipment is certified and marked in conformance with this location. Request a certificate of compliance provided by a Nationally Recognized Testing Laboratory (NRTL) stating the location where the equipment can be used.

Regarding the second aspect you need to define the type of hazardous waste the vacuum cleaner will be used for (type of dust or liquid) and the quantity to be collected. Based on this information, and depending on the hazardous properties of the waste, you’ll have the choice between two main types of collection systems:

“Dry type”: collection of the waste inside a bag or directly inside the recovery tank

“Wet type”: precipitation of the waste into a neutralizing liquid bath (recommended for self-heating waste for example)

Read the vacuum cleaner’s instruction manual in order to validate the application it was designed for.

Different sizes of equipment, carts models and recovery tank emptying systems are available.

Vacuum cleaners certified for use in hazardous locations are offered in both electrical and non-electrical (compressed air driven) versions. Vacuum cleaners using compressed air are usually less expensive to purchase and to maintain than electrical ones.