Is your business handling any of the following materials in powder form: aluminium, coal, custard, magnesium, nylon, paper, polyethylene, polystyrene, sawdust or sugar? If so, are you aware of combustible dust hazards, especially the destructive nature of secondary dust explosions?
The list of materials detailed above is not exhaustive, but shows a number of common materials in the powder form, which can generate a dust explosion hazard.
It is now over ten years, since there was a sugar dust explosion at Imperial Sugar, Port Wentworth, USA which killed fourteen and approaching three years since the wood flour dust explosion at Wood Flour Mills, Bosley, UK which resulted in four fatalities.
As an insurance risk control engineer, it is important to recognise the occupancy hazard of combustible dust and what to look for on-site. For there to be a fire or explosion, caused by a combustible dust, there needs to be five components which are the fuel, oxygen, source of ignition, dispersion and confinement of the dust.
There are standard laboratory tests available to verify if a dust is combustible and the classification of the dust explosion class. My recommendation to insured’s is to have samples of dust tested to check the characteristics of dusts, as experience in testing has shown the majority of all fine powders are combustible.
A primary dust explosion is bad enough, however, it is usually a larger secondary dust explosion, which causes significantly more damage. This being due to the primary dust explosion, often causing the dispersion of a larger amount of dust (i.e. fuel), if the dust has been allowed to accumulate.
If you have any horizontal surfaces and are handling combustible dusts, have you checked your process for any high level dust accumulation or any dust accumulation within any roof void areas? These are areas, which will often be audited during an insurance survey.
There are a number of simple steps which can be taken to reduce the potential of a combustible dust incident:
- Employees including workers and managers need to be aware of dust explosion hazards and recognize the serious nature of dust explosion hazards, especially secondary dust explosions.
- Routine housekeeping inspections should be undertaken to monitor dust accumulation, and in the event of an accumulation of combustible dust, this needs to be safely removed. The use of compressed air to displace accumulated combustible dust is not recommended.
- Any plant handling combustible dusts should where practicable, minimise the number of horizontal services where dust can accumulate.
- Process equipment handling combustible dusts, should either be designed with a pressure rating suitable for a dust explosion or be fitted with appropriate overpressure relief and blowdown protection.
- The potential for dust explosion propagation through connected items of equipment needs to be considered at the equipment design stage and during any hazard and operability study.
- The dust explosion hazard should be captured within the Fire Risk Assessment and DSEAR (Dangerous Substances and Explosive Atmospheres Regulations) assessment.
During my time in insurance, I have observed a number of potentially hazardous dust accumulations, worked with insureds on improving their process safety management by having representative samples of dust tested to confirm whether they are combustible, provided assistance on the over-pressure design rating of process equipment and continued to share my knowledge on this important occupancy hazard.
Stuart Kenyon, AVP Risk Control