Combustible Dust- Housekeeping Programs

As the CEO of a large manufacturing company, you are concerned about your employees being at risk of injury while cleaning combustible dust accumulations. You have heard lots of horror stories and you are not sure of which is the truth. How should you proceed?

Firstly, it’s crucial to assess the materials used in the manufacturing process to determine if they are known to produce combustible dust. Following this, a thorough inspection of the facility and see where and which dust is accumulating. It is important to note that not all dusts are combustible, for example companies that sand their parking lot during winter months may find deposits of non-combustible road sand dust inside large overhead doors.

Once you have determined the types of dust present and the sources of the dusts, you have two options.  The first is to have the dust tested at a dust laboratory for combustibility, usually a GO-No-Go test will confirm or deny the flammability of a dust sample. The second choice is to assume it is combustible. If you choose to test your dust you can also have additional tests done to determine combustibility characteristics such as Minium ignition temperature (MIT) or Minimum ignition energy (MIE) to assist you with selecting the appropriate control measures and developing safe work procedures for safe handling and cleanup activities.

Once you understand the combustibility parameters you can design the best way to manage the cleanup activities.

In order to manage the hazard effectively you need to monitor and document where the dust is accumulating and how fast it is accumulating so you can design activities to remove it effectively, before it reaches hazardous levels.

 Once you have a monitoring system in place, you can identify where your process emits dust and where the sources are located. This allows you to start developing strategies to collect the dust at source. As you implement solutions to decrease dust escaping from the process you should be able to see it in your monitoring data and adjust your cleaning frequency accordingly.

To determine the frequency of cleaning you have to be aware of the specific density of your dust, this will determine the allowable layer depth of accumulation. For wood dust 1/8” is practical for metal dust 1/32 “is the accepted standard.

 It is best to clean areas before this level is reached, this allows areas to be cleaned without generating dust clouds that could reach the MEC (Minimum Explosible Concentration).

Before cleaning activities start it is recommended to scan the area around the proposed cleaning zone with a thermal imaging camera to ensure that equipment has been allowed to cool and there are no overheating components, electrical shorts or other ignition sources present.

When cleaning pipes and beams it is recommended to use extendable brushes and vacuum attachments to allow workers to stay on the floor instead of working off of ladders. When dislodging dust from pipes or beams the worker should never be in the path of falling dust.

When cleaning dust accumulations it is recommended to be aware of the relative humidity. When the relative humidity drops below 45% RH there is an increased ignition risk from static electricity, and fire behavior is much more aggressive. This can be reduced by misting activities, or postponing cleaning activities to coincide with a higher relative humidity.

When conducting cleaning activities, it is important to coordinate activities so that cleaning activities and work that generates ignition sources such as welding and grinding (hot work) or electrical maintenance are not occurring at the same time in the same place.

There are several ways of removing dust from elevated surfaces, vacuuming is the preferred method but is not always practical, sweeping and brushing is effective in certain locations and the last resort is compressed air. If compressed air blow down is the only viable option, then a specific safe work procedure should be documented and followed to ensure that ignition sources are controlled and dust clouds are not created. It is critical to only use the minimum air pressure, and clean small areas completely before moving on to the next area.  

When working with combustible dust it is crucial to ensure that employees and contractors are aware of the hazards present and the procedures to follow to complete their tasks safely.  Providing training in safe work practices and emergency procedures is paramount to ensuring that people are not injured as a result of improper use of compressed air, fire extinguishers or straight stream fire hose nozzles.

This article is not intended to be a definitive guide to housekeeping practices but just a primer to allow People to become more aware of the components of an effective housekeeping program, and to understand which questions to ask when seeking assistance with setting up a program.