Mechanical Equipment Selection in Hazardous Areas

Why Mechanical Equipment Selection Still Causes Issues

The implementation of DSEAR way back in 2002 placed a requirement on employers to formally manage any ignition sources that could be created from mechanical equipment operating in an atmosphere where combustible dust could be present (i.e. hazardous areas).

In the last 20 years, industry has ironed out many of the early teething problems and the selection and lifecycle management of mechanical equipment in hazardous areas is now trouble free and well understood.

Well, there are still issues. This article will point out some golden rules to help unpick user requirements when it comes to managing mechanical equipment installed where combustible dusts are present.

“If you can eliminate accumulation of dust in a plant, you may be able to remove external Zone 22 areas.”

Step One: Eliminate the Need for a Zone

This may sound a strange question but it’s the first thing you should look at following Regulation 6 of DSEAR which puts a responsibility on operators to eliminate flammable atmospheres where possible. This is easier if you are still at the design stage of a project but even mature processes can look into elimination and/ or reduction of risk.

When considering combustible dust hazards, one of the most fundamental things that can be done is ensuring that housekeeping is good. If you can eliminate accumulation of dust in a plant, you may be able to remove external Zone 22 areas.

This offers benefits in no longer then needing certified equipment but accumulations of dust can lead to secondary explosions in a process disturbance. It is these secondary explosions that can result in multiple fatalities (Imperial Sugar, Bosley Wood Mill) and so removing this hazardous scenario should always be a priority.

Figure 1 – Dust accumulations. External Zone 22 may be required  – Housekeeping improvements would be preferable!

Secondly, it is common to see external Zone 21 areas around hoppers and bag handling processes. But ask yourself, how credible is it, during normal operation, to have a dust cloud with a concentration that would result in a dust cloud that you could not see through? If this is the case? How does the operator breath?

Most dusts have a minimum explosive concentration of around 30 g/m³. This would be an optically dense cloud and obviously impractical to work in. In fact this level is many orders of magnitude higher than the threshold for dust exposure in the COSHH Regulations. However almost all dust handling equipment will have in internal zone, even if there isn’t an external zone where the equipment is installed.

So, before you spend time and money on certified equipment, check that it is needed.

“The more information you provide the more likely you will get the right equipment for the zone of use.”

Specifying the Right Equipment for Dust Zones

So, you have established that there is a zone, either a Zone 22, 21 or 22. The next challenge is to establish your dust group and temperature rating. The dust group, IIIA, IIIB or IIIC isn’t too hard to establish. Conductive dusts are IIIC and nonconductive ones IIIB. If it is a flying or fibre, it is IIIA.

A bigger challenge is establishing the temperature rating. This is worked out from the layer ignition temperature and cloud ignition temperature and it’s finding these parameters that can be a challenge. The Safety Data Sheet (SDS) for the dust, if you are lucky, might give you an auto ignition temperature but it may not be clear which form of dust this is for.

Once you find these metrics, the temperature limitation is the lower of the layer_5mm ignition temperature minus 75 K and the 2/3 of the cloud ignition temperature.

You now have enough information to allow a supplier to specify equipment for you. They will need the equipment category (equipment protection level (EPL)), dust group and maximum allowable temperature. And they will require this for the internals and externals of the equipment.

It is important to note that as a customer, you should tell the supplier the category (EPL) of equipment (1D (Da), 2D (Db) or 3D (Dc)), not the zone. This is because you can install either over or underrated equipment for a zone if a risk assessment is carried out to justify this. The more information you provide the more likely you will get the right equipment for the zone of use.

The information relevant to the certification of the equipment will be on a nameplate and duplicated in any certification or documentation (Declaration of Conformity/ Incorporation) sent with the machine.

Understand Manufacturer-Specific Safety Requirements

Almost all mechanical equipment will be built to BS EN 80079-36 (Explosive atmospheres Part 36: Non-electrical equipment for explosive atmospheres — Basic method and requirements) and BS EN 80079-37 (Explosive atmospheres – Part 37: Non-electrical equipment for explosive atmospheres – Non-electrical type of protection constructional safety “c”, control of ignition source “b”, liquid immersion “k”).

This means that unlike electrical equipment, the protection concept will require manufacture specific maintenance, installation or operational requirements to ensure that the equipment remains safe through its lifecycle.

This can result in very onerous conditions of use. Examples can be the installation of protective instrumentation (temperature monitors, vibration trips, etc.), the imposition of specific operating conditions and the burden of very strict maintenance requirements. Examples of this can include the replacement of bearings on a 6 monthly basis.

Many of these safeguards may well be appropriate and necessary however, it is important that as an end user, you understand these requirements before committing to buying. You may operate a continuous process so the last thing you want to do is impose a shutdown every 6 months to change components.

Not only will this disrupt production but if a bearing is working well, the worst thing you can do is strip a machine apart and rebuild it with a few added faults! Plus after a few years, will production be happy to shut down when you never find any faults in the bearing? Can you approach the manufacturer and suggest an alternative such as condition monitoring? Or even look for an alternative supplier.

If additional instrumentation or mechanical safeguards are needed, you want to know about these whilst the plant is being constructed, nit when you read the instruction manual during commissioning.

“Not only should maintenance technicians be aware of their responsibilities and requirements under DSEAR, but they must also be technically proficient overhauling that equipment.”

Commissioning: Getting it Right the First Time

Regulation 7 of DSEAR places a requirement on the end user to ensure that everything is suitable and safe before use. For mechanical equipment, this will include ensuring that the machine has been installed, inspected and commissioned correctly. The O&M manual may well list some of these requirements including initial vibration checks, belt tensioning or the filling of oil.

If the equipment is supplied on a skid, there may be a number of equipment items making up the assembly. It is your responsibility to ensure that any overall certification is a worst case.

What this means is that if the skid has a certification of 2G, T200 IIIB, there shouldn’t be a lower standard of equipment on the skid. For example if there was a rotary valve with name plate saying 2G T250 IIB, this would not be acceptable as it has a temperature rating that is too high.

Ongoing Maintenance and Responsibility Under DSEAR

As mentioned previously, unlike electrical equipment, there isn’t a standard dictating the hazardous inspection or maintenance requirements for mechanical equipment but guidance is provided by CompEx (Non-Electrical Inspection Schedule CCL 7003, Rev 4 05/24). What you must also do is to extract any maintenance information from the O&M manual and ensure that this is carried out.

There may also be specific parts that are requiem so rather than using generic off the shelf components, do you need to buy spares from the OEM?

Technical competence needs to be verified. Not only should maintenance technicians by aware of their responsibilities and requirements under DSEAR, but they must also be technically proficient overhauling that equipment.

Do they need extra training from the supplier?
What about using third parties?
What standard of spares are they using, are they reverse engineering parts?
How do you control this. Remember, you can delegate your tasks but not your responsibilities.

Recap: Your Checklist for Safe Mechanical Equipment

Something to remember with mechanical EX equipment is this simple route to success:-

• Ensure the zones (inside and outside) are right.
• Ensure the equipment specification is correct.
• Check the special conditions of use.
• Check you have received what you ordered!

Make sure you maintain it correctly and document.

FAQs: Mechanical Equipment in Dust Hazard Zones

Do I always need a hazardous zone classification for dust?
Not necessarily. If dust accumulation can be prevented especially through good housekeeping a zone may not be required

What are the benefits of avoiding a Zone 21 or Zone 22 designation?
You can avoid the need for certified ATEX mechanical equipment and reduce the risk of secondary dust explosions

What is the difference between dust groups IIIA IIIB and IIIC?
IIIA is fibres IIIB is non-conductive dust and IIIC is conductive dust which presents the highest ignition risk

How do I determine the temperature rating for my equipment?
Use the lower of the 5mm dust layer ignition temperature minus 75K or 2/3 of the dust cloud ignition temperature

What equipment details do suppliers need?
You must specify the EPL category dust group and maximum surface temperature for both internal and external zones

What are the implications of BS EN 80079-36/37 compliance?
Equipment may have specific installation operational or maintenance requirements that must be met to remain safe

Why is it important to check equipment documentation at commissioning?
To ensure installed components meet the certified specification and there are no mismatches in temperature class or gas group

Can I substitute OEM parts with generic components?
Not always. OEM parts may be required to maintain equipment safety integrity especially under special conditions

Are there training requirements for maintaining mechanical Ex equipment?
Yes. Technicians must understand DSEAR responsibilities and be trained to overhaul equipment to certified standards

Can third-party service providers be used?
Yes but you must verify their competence and ensure that parts and processes meet original certification requirements