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The Howie Report

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PROPOSAL FOR REVISED TECHNIQUES IN AIR EXTRACTION FOR MINIMIZATION OF AIRBORNE FIBRES

Since publication of the Howie Report there have been renewed concerns about fibre levels in the work area when removing asbestos. Powered respirators have been shown to be far less effective in actual use than previously supposed, with Nominal Protection Factors of 2000 being reduced 50 times to produce Workplace Protection Factors of just 40. Robin Howie recommends that powered respirators should not be worn whenever the exposure level within the work area exceeds 4 fibres per ml - or EVER in a hot environment. Currently this leaves Positive Pressure Demand Valve Supplied Air Systems (i.e. air supplied by hoses from a compressor or from bottles) as the only viable form of Respiratory Protective Equipment (RPE) available under these circumstances.

However, it is important to remember that all forms of Personal Protective Equipment (RPE) are intended as the LAST means of defence to be provided by the employer for the worker, all other means of ensuring the maximum protection of the operative should have been utilized first

The writer accepts that circumstances will arise where it is absolutely impossible to close down all the boiler room or steam pipe plant from which asbestos has to be removed, and under these conditions Supplied Air will be the only way to proceed; but it should be noted that with the benefit of a compressor the air can additionally be used, via air-fed suits or vests, as a cooling device making the operatives MORE productive and eliminating the risks from heat-stress.

As far as the normal cold strip is concerned there are a variety of engineering techniques which can be employed to ensure the minimum number of airborne fibres:

1) WETTING - Although this has become increasingly popular in recent years, there are many occasions where it could be utilized but is avoided by the contractor for the erroneous reasons of cost or convenience. Manufacturers of the surfactants can demonstrate that a properly managed wet strip can actually be cheaper by virtue of reduced cleanup times and earlier clearance tests than a dry strip.

2) GLOVE BAG TECHNIQUES - The use of glove bags as a secondary containment within the work area, with local extraction by means of a HEPA vacuum is a sure way of reducing fibres. We DO NOT recommend the use of glove bags as a primary containment except where the purpose is purely the minor temporary repair of otherwise safe pipe insulation AND then only where a PVC glove bag is used (Polythene ones are much more prone to puncturing by dropped/clumsily wielded tools etc. and should only ever be used as a secondary containment).

3) INCREASED AIR EXTRACTION - On the average abatement contract, a negative pressure of between 20 and 30 Pascal’s (2-3mm or .08-.12"wg) will be required and unless the work area has been very securely sealed (which would entail methods superior to the normal tenting with polythene sheeting) this will achieve 4-6 air changes per hour. This should be regarded as the absolute minimum to attain a reasonable flow of air and entrapment of fibres. In my experience this is more extraction than is seen on most contracts and can only be ensured by the use of additional air movers and differential pressure monitoring equipment. The movement of air directly across the work area is most important and it is vital that smoke testing is also done to ensure that air is moving throughout the containment with no stagnant areas. Much thought should be given to the location of the extraction point (ideally all air movers should be located together, and this location should be diagonally opposite where most of the make-up air is introduced (normally the airlock). If there are separate airlocks for personnel and equipment/waste removal, they should be adjacent to one another and the extraction point should be at the furthest point and not directly opposite to ensure maximum air circulation. Various techniques for the management of the air which include forced introduction and local extraction or air across the workface can be considered, but it must be remembered that to produce a sufficient negative pressure for safety this will mean even more extraction and it is absolutely essential to have an additional air mover on standby linked to automatic start-up from the negative pressure monitor in case an extractor goes down, as this could lead to a catastrophic pressurization of the work area and escape of fibres.

4) RECALCULATION AND LOCAL FIBRE ENTRAPMENT - Normal HEPA filtered air movers intended for extraction should never be located within the work area as it is impossible to fully decontaminate the machines, they should remain outside with the filter face secured in the tenting membrane. In order to maximize air circulation they can often be fitted with one or two satellite pre-filters that can be positioned within the area and connected to the extractor by means of flexible ducting to ensure no areas of stagnant air are bypassed. In America, where containment areas are often bigger than is the norm in the UK, we pioneered the concept of re-circulating air movers. These are cheaper, fully waterproof and decontaminatable machines, normally fitted with 95% efficient filters, and can be located in the containment area to keep the air moving in an onward direction towards the extraction points while entrapping fibres and reducing exposure levels at the same time. Our company attempted to introduce these to the European market some years ago and were met with universal disinterest, however, in view of the renewed concerns for fibre reduction, we are reintroducing this concept as a valuable engineering technique in which we hope there will now be more interest.

 

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