Assure 360

DCU safety – reviewing the guidance for safe decontamination

Written by Nick Garland on 16/01/2020
 

We all know that the job of asbestos removal is dangerous – that’s why it’s so tightly regulated. But while the most serious risks are often found inside the enclosure, they don’t stop there. The decontamination unit (DCU) presents its own hazards – from asbestos exposure, through electrical and gas hazards, to crush injury when setting up or decamping. So what guidance is available, and how can it help keep operatives safe?

Last year the Asbestos Leadership Council (ALC) made time in several meetings to discuss DCU safety. Unfortunately they’ve made slow progress in producing guidance, and the final version hasn’t been issued. That said, I wanted to take a look at what there is so far, as it’s good stuff.   The focus is on electrical and gas safety, which is particularly welcome – working practice in much of the industry is still based on very outdated facts and guidance.

I’m also adding in some additional observations based on my experience of the biggest hazards, and the safe working practices designed to mitigate them.

Gas safety

Manufacture

The guidance starts predictably enough, instructing that gas boilers should meet the required BS EN standards, that they should be installed by an accredited gas fitter, and that each appliance should be fitted with an isolating valve and flame failure device. However, it then goes on to say that all boilers situated in the clean end – rather than a sealed cupboard – should be of the balanced flue type     .

For those of us who aren’t gas engineers, in a balanced flue (also known as room-sealed) boiler, the entire combustion circuit is sealed off from the room that the boiler’s in. The fresh air supply, combustion chamber, heat exchanger and exhaust gases are open to the atmosphere only, meaning that if something goes wrong, any toxic or flammable gases should be vented out of the DCU.

Insisting on this type is wise, as they’re much safer than open flue boilers which draw their combustion air from the room they’re in, but following the guidelines might mean an expensive upgrade for any older DCUs.

There are some other issues to pick up on. If the boiler is mounted in a separate sealed cupboard it is best practice for that boiler to be room-sealed anyway, but regardless the cupboard door must be closed and sealed at all times. Many times I’ve seen cupboard doors left open, sometimes for convenience, but sometimes because there is otherwise insufficient ventilation in the cupboard for the boiler to work. If the boiler only works when you leave the cupboard door open, then it’s effectively in the clean end, and must be room-sealed.

It’s important to understand that a room-sealed boiler doesn’t guarantee that combustion products like carbon monoxide (CO) can’t leak into the room. Seals can fail, so there should always be a CO alarm fitted in the clean end, adjacent to the vent to the shower compartment. Correct positioning is important – I’ve seen random locations, not all of which will be effective according to the guidance.

Gas Bottle Storage

The guidance here pretty much summarises existing standard guidance. In brief, the gas bottle(s) should be:

  • External to the DCU
  • Vented to the outside
  • Labelled as carrying flammable gas
  • Positioned vertically
  • Propane rather than butane (which has issues below 5oC)

Note, too, that there should be a maximum of two 16kg bottles, and that nothing spark-generating should be stored with them.

So far, so standard, but then we get to areas where I’m not sure we have much compliance. Gas bottles should be:

  • Ventilated top and bottom, with a minimum area of 50mm2, or 1% of the floor area (whichever is greater)
  • Separated from the clean end by a barrier with a half-hour fire rating
  • Secured rigidly top and bottom
  • Connected to a date-stamped, British Standard-compliant low-pressure regulator and hose
  • Kept in the enclosure during use

Gas Safety Certificate

There’s some welcome clarity here: DCUs require mandatory 12-monthly gas-safety certificates. Some HSE inspectors are still referring to a very old note that mandated six-monthly inspections for open-flued units. This detailed guidance supersedes and clarifies this.

Normal operation

In day-to-day use, the gas pipework needs to be checked daily and at the end of the project – not a job that I’ve seen on many supervisor checklists. There should also be emergency procedures to follow if gas is smelled. The advice states that gas should be isolated at the end of the shift, but it then goes on to contradict itself, suggesting that if there’s no oil-filled radiator the pilot light should be left running in cold weather. Presumably this will be cleared up in the final pre-publication checks.

All vents, clearly, need to be kept clear. If you have an open-flue boiler in a sealed  cupboard, that cupboard needs to be kept closed and the seals must be in good condition. In all cases the CO alarm must be checked at least weekly.

Electrics & Earthing

This is usually the area that gets the most attention when a job is audited, but the justification for this seems patchy at best. To my knowledge there has never been a DCU electrocution, so the previous guidance has clearly been serving us well.

This guidance states that all DCUs must regularly be electrically inspected and tested    – we rarely see units that haven’t been. In fact, the biggest risk is likely to come from using the client’s mains supply if it turns out to be faulty. The moment of greatest risk is brief – when an individual is standing on the floor, but touching the metal frame of the DCU.

The guidance offers some pointers on how to eliminate electrocution risks:

  • DCUs should be protected by a residual current device (RCD)
  • Earthing should be independent of any client supply, via copper rod. This should be driven in to the ground by some distance, which itself raises hazards that should be protected against
  • You should investigate the maintenance of the client’s electrical supply
  • Power sockets used as a source should be checked with an ‘advanced plug-in socket tester’

However the guidance really calls for better design of DCUs to ensure better electrical separation, along the lines of a bathroom. Generally there should be layers of insulation between electricity and people, and the power for recharging masks should come from two-pin, low-voltage sockets. Where there are concerns about the quality of the source electrical supply, it’s perhaps wisest to use a single-phase generator rated below 10kVA, which doesn’t need earthing at all.

Movement and positioning

The ALC’s guidance may be useful and comprehensive, but it overlooks the most pressing DCU safety issue: the risks relating to manual handling and vehicle movements when positioning them. DCUs are heavy beasts, and it typically takes more than one person to maneuver them by hand. It takes coordination and well-designed procedures to prevent workers being trapped or injured, yet it’s all too often overlooked.

I personally know of one serious injury that has occured due to lack of concentration when maneuvering a DCU. The following is the safe working procedure that was created after the event:

When positioning, re-positioning or removing a DCU from site it is critical that it is done so safely. DCUs are heavy pieces of plant. They can cause injury by trapping operatives against fixed structures, and can become unstable if moved over rough ground.

  1. The route that the DCU will be moved over must be checked. It must be level and clear of obstructions. Hazards must be removed / corrected prior to moving the DCU
  2. One operative is to hold the hitchcock and handbrake to steer. This operative oversees the manoeuvre and will instruct all those assisting
  3. A maximum of three operatives will position to the rear of the DCU, and will be instructed when to push and stop as the DCU is being moved. At no point is anyone to use the two front handles on the DCU for pulling the DCU from the front
  4. The DCU will be guided to the van and hitched onto the van
  5. Driver to check electrics before moving away

Where necessary – a traffic marshal will use a barrier to stop traffic when the DCU is to be moved into the road to be hitched onto the waiting van.

It’s a shame that the ALC’s guidance overlooks the risks from positioning the DCU, but apart from that it’s a helpful guide that helps clarify what’s necessary to ensure safety as operatives finish shifts. Well-trained staff should already understand that the risks of asbestos removal don’t end until they’ve decontaminated and exited the DCU (and beyond) – following this guidance should help ensure they stay safe while they do so.

Tweet  Share on Facebook  Share on Linkedin