Our View on The complexities of Dust DSEAR Risk Assessments

Area classification and DSEAR risk assessments for combustible dust environments varies drastically from that of gases/ vapour environments. Most of this awareness comes with carrying out many of these assessments in different industries. Some of the key differences we have noticed when carrying out these assessments which makes them particularly complex and challenging:

There are (pretty much) no calculations you can do for dust cloud zoning assessments.

Most zone extents come from guidance in the standards (BSEN60079-10-2) or from site observations. This means using an experienced assessor is critical, as they will be able to compare to other situations and understand the potential failure modes more readily.

Is my dust even combustible?

This is a common problem when dealing with novel solids or ones with particularly poor MSDS's (safety data sheets). We have come across MSDS with no mention of combustibility but when the supplier is probed on it, they admit there may be a risk of combustible clouds forming. To correctly specify equipment to handle the dusts, or to be in any dust zones created you will need to establish the explosion properties including the overpressure the dust can develop (so you can specify equipment to contain an explosion, for example) and the auto ignition and dust layer ignition temperatures (for specification of equipment temperature limits).

A good way to check if your dust is potentially flammable is to search for it (or similar materials) on the German GESTIS-DUST-EX database. This can often yield exactly what is needed for your situation. We have found numerous times it to be a fantastic resource for a quick review of whether a material could be combustible and if you find a match for what you're using, it can be used for the properties of materials lists required in the HAC study. Failing that, and if you really need to be sure of your particular properties, you will need to get the dust tested for explosion properties. A potentially daunting task, there are several specialists here in the UK offering these services.

A basis of safety of "explosion venting"

Because of the difficulty in excluding all ignition sources when dealing with dust handling systems, right down the bottom of the hierarchy of control there is the option to vent an explosion safely, away from people. This options isn't generally acceptable on gas/ vapour systems and provides a final route to a basis of safety if none of the other options are viable (and deals with the tricky issue of foreign bodies in dust handling systems that no amount of magnets can get rid of).

An improvement in housekeeping can have a major impact

We risk assessed one facility who had got their dust layers checked for flammability. With the dust covering large areas of multiple levels of a large facility, it would have almost bankrupt the company to upgrade all their equipment to being suitable for dust zones. Instead, a pragmatic solution was to implement more thorough and audited housekeeping regimes, to keep on top of dust levels and therefore declassify the whole of the area, except where small secondary zones existed. This can be a very good reason to do your DSEAR RA first, before attempting to do area classification zoning, as you would otherwise have to revisit the zoning once improvements identified in the risk assessment are implemented.

The secondary explosion risks can be huge

When a large area is covered in even a small surface layer of combustible dust, the potential impact of this dust and the resultant explosion can be catastrophic if dislodged in the presence of a source of ignition. There are no shortage of industry examples of secondary explosion events. From a P&ID and desktop risk assessment often you simply cannot grasp the potential magnitude, which means that for dust facilities a site visit is always a must for DSEAR Risk Assessments (no matter what the Covid travel restrictions might be!). The closest analogy for gas/ vapour systems would be pool fire events, leading to fire relief of other equipment and potential overpressure events, but again these are fairly predictable for gases and vapour risks compared to dusts.

We are fortunate to have had experience carrying out DSEAR risk assessments in a variety of industries handling dusts such as food, distilleries, waste management, general manufacturing, pharmaceuticals and speciality chemical sectors. This means we can provide a very broad range of potential solutions and improvements to most DSEAR studies we undertake to help clients protect their people and assets.