In today’s episode of the Dust Safety Science podcast, we go over the reality that controlling dust hazards is not the same as removing them entirely. These Safety Shares episodes cover topics that people send in through the HelpDesk. The dust hazards question is the result of emails Dr. Chris Cloney received from listeners in Canada and the UK.
An article from Canada mentioned an appeal for occupancy classification for a flour mill in British Columbia. Another incident that came through was one from the UK where a vapour explosion occurred in a mixing tank of a hair products manufacturer. Vapour extraction was in place, but it wasn’t sufficient to control the hazard.
A dust hazards analysis (DHA) is all about determining what hazards exist and answering the following questions:
- What are the existing safeguards and controls in place?
- Are they in compliance with the NFPA standards or whatever standards that you’re testing against?
- Are they sufficient to ensure the safety of employees involved in the operation, operational continuity, and minimize loss of products and other operational goals of the facility?
Hazard Control vs. Hazard Removal
There is a concept of inherently safer design, where you want to look at minimizing or removing, substituting, moderating or simplifying the hazards. However, most of the time we’re talking about other elements of the hierarchy of controls, which includes engineering design controls and administrative controls. In these cases, however, the fact remains: putting the control in place is not removing the hazard.
Take the example of a saw. If you have a saw blade that’s spinning and you put an engineered guard in front of it so that person can’t stick their hand in, you didn’t remove the hazard, you just put a control in place. People who are working in that area need to be aware that the blades are still behind the guard, and even more aware of the times when the guard may fail. There are still a lot of things that can go wrong because a hazard remains.
By believing the hazard has been eliminated just because the control has been installed, you are much more vulnerable when the control fails. Let’s examine these two examples to see how they relate.
Flour Mill in BC: Occupancy Classification
In February 2020, an appeal took place before the British Columbia Appeals Board. It was a request to have a flour mill reclassified from a high-hazard industrial occupancy to a medium-hazard industrial occupancy.
In this case, there was a two-storey building with multiple suites and businesses, and one of those suites contained a flour mill. The room measured approximately 10 x 10 metres. This plant has a production capacity of 1.5 tons of finished flour per hour from two tons of grain, and operates nine hours per day. Although it’s not a large processing operation, it produces a lot of flour on an hourly basis, enough to create combustible dust hazards.
The mill did have dust collection equipment. It was designed to contain the dust within the equipment, and they managed any primary explosion issues through explosion venting ducted to the exterior of the building.
In British Columbia, high hazard industrial occupancy means that it is an industrial occupancy containing sufficient quantities of highly combustible or flammable or explosive materials which, because of their inherent characteristics, constitute what’s known as a special fire hazard. A medium hazard industrial occupancy means an industrial occupancy in which combustible content is more than 50 grams per metre cubed or 1200 millijoules from your square floor area, and it’s not classified as high hazard industrial occupancy. This relates to the fire risk in that facility and how much combustible material is actually stored there.
This particular flour mill was deemed to be high hazard. It had sufficient quantities of highly combustible, flammable and explosive flour dust, and its inherent characteristics constitute a special fire hazard. The argument made by the company was that they had the equipment in place to manage and control dust accumulation. Due to the features that they had there to eliminate the risks of fires and explosions, they should not be considered a special fire hazard.
The Canadian source sent this information to Dust Safety Science because the British Columbia Appeals Board had ruled that this was indeed a high hazard occupancy. It was consistent with the definition of high hazard occupancy and mill owners did not provide sufficient information to demonstrate otherwise.
Vapour Flash Fire in UK Chemical Company Mixing Tank
This incident was investigated by the Health & Safety Executive in the U.K. The company was fined £480,000 after one of its workers sustained what they termed “superficial burns” at the factory. These were burns to his upper torso, right arm and hand.
In the processing operation, the worker added powders to a 10,000-liter stainless-steel mixing tank. The process involved pumping ethanol directly into the tank via pipework from an external storage tank. The other materials, including the powders, were added and heat was applied. The vessel also contained a steam coil that was used to mix the material in the heat. The company did have an extraction system at the lids’ lip to remove vapours but it was not an adequate control measure to prevent the buildup of the flammable atmosphere.
The article we received talked about the gas explosion. They didn’t mention the powder being added at all. So in this case, we’ll just assume it was a vapour cloud explosion. The theory in that article, at least, is that vapour did build up over the headspace of the tank. When it ignited, it caused the worker’s injury.
The initial penalty was £720,000 but it was reduced when the company pleaded guilty to breaching regulations with the DSEAR – the Dangerous Substance and Explosive Atmosphere Regulations in the UK.
In the case of the vapour flash fire, we still had the hazard. A control was put in place and it would be incorrect to say that that hazard no longer existed. A flash fire happened and an Individual was injured. You’re not removing the hazard just by putting engineering controls or even administrative controls in place – the hazard is still there
When you start to put controls in place, you actually need to have an increased sense of vulnerability about these types of hazards. Instead of saying this hazard doesn’t exist, we need to say, “Well, we have this control in place to protect from this hazard.”
It’s important to give more thought to employee training. In that way, if they do have an upset condition or a normal condition where they’re even opening up the equipment and inerting systems, they have the awareness and knowledge and understanding to make smart decisions about how to actually go about doing that work.
If you say the hazard doesn’t exist because you put that control measure in place, you’re much less likely to train and your employees are much less likely to approach it with a sense of vulnerability. You’re also much less likely to maintain those controls over time, and eventually something will happen.
Conclusion
It would be great if we could look at more intrinsically safe design aspects of combustible dust, and share those with the community. Nevertheless, when it comes to preventing explosions, we’re talking a lot about control measures. In all those cases, that hazard has not been eliminated – it still exists. The more people are trained on this subject, the better they’ll be able to understand what can happen when the controls are down.
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Dust Safety Share
Rulings
British Columbia Appeals Board
Articles
Chemical Firm’s £480k Fine After Vapours Ignite Causing Worker’s Burns
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