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When should Respiratory Protective Equipment (RPE) be worn to control exposure to Respirable Crystalline Silica (RCS)?

RCS Respirable Crystalline Silica is hazardous to health: it can cause Occupational Asthma, COPD and Silicosis.

 

The control of Substances Hazardous to Health (COSHH) Regulations 2002, as amended 2004, require employers to assess the health risks and precautions needed to prevent or control exposure to hazardous substances such as R.C.S. 

 

The Regulations also prioritise the order in which control measures should be applied (COSHH regulation 7(7)(a), Schedule 2A) RPE is a last resort measure, the first priority should always be to prevent exposure or, if this is not possible, ‘to control it at source’, for example by effective local exhaust ventilation.

 

The measures that should be considered and the priority order in which they should be implemented are:

 

PROCESS CHANGES

 

It may be possible to change the process in terms of replacement of stone with one containing less RCS. This option could be limited due to customer requirements (particularly relevant in restoration work). If this is not possible, more initial dimensioning (shaping) on the stone using primary and secondary cutting saws prior to handwork using power tools may help reduce individual exposures. Reducing the use of hand held power tools may also be an option.

 

SEGREGATION

 

High risk processes should be segregated where possible. Access should be prevented, entry only for authorised persons with RPE. Primary and secondary saws can be remotely operated and personnel should be excluded from the area where possible. Processes involving the use of power tools e.g. disc cutting, polishing, pneumatic chiselling should also be segregated where possible. Only in extreme circumstances where there are few or single employees or tasks are very short would segregation not be considered necessary. 

 

SUPPRESSION - Wet Working

 

Even where there is segregation or provision of LEV it is recommended water is used to suppress the evolution of dust; either by wetting the stone or by providing a water stream onto the blade or disc during cutting. In primary and secondary saw cutting water jetting is used as the primary control in addition to segregation of the process. When using hand tools the use of water jetting should be considered where possible (may not be an option where electric tools are used).

 

Where water jetting is not possible the stone should be kept wet and dry working should be avoided. Where running water suppression is provided it is recommended that where water impacts on surfaces the surfaces are coated to reduce the generation of mists (e.g. Astroturf or similar to line surfaces around primary saws). The clearing and removal of the stone slurry will need to be managed and operators will require protective clothing to keep them dry and warm. It is likely that RPE will still be required when water suppression is used.

 

LEV (LOCAL EXHAUST VENTILATION)

 

Booths

 

High risk processes using hand held power tools should be carried out in a ventilated booth. These include disc cutting, disc polishing, pneumatic chiselling. For hand chiselling where high silica stone and duration of work is in excess of 1 hour a ventilated booth is preferred although an effective and properly used capture hood could be used in some circumstances. Operator should be trained in the effective work practices to be employed when working in the booth e.g. position of the work piece, use of the tools to ensure dust jet is directed to the back of the booth, use of open framed, rotatable ‘banker’, use of other controls if necessary etc.

 

Capture hoods
 

These are far less effective than booths and should not be used for high speed power tool operation e.g. disc cutting, disc polishing or sanding unless for very short duration work on small workpieces and very low RSC stone. They may be of limited use for pneumatic chiselling, but can be used for other hand held tool work. The hood should be positioned as close to the point of origin of the dust, the hood ductwork should allow easy placement close to the work and the operator should be aware of the effective capture distance of the hood. A rotatable ‘banker should be used. Where hoods are used wet working is recommended and additional use of a high standard of RPE is likely to be necessary.

 

On-tool extraction
 

This can be more effective than capture hoods where straight lines or flat surfaces are being worked. The blade should be totally enclosed by a hood, guard or brushes and these should be well maintained. On-tool extraction is limited where there are curves, bends or uneven surfaces being worked or where work is at the edge of the stone. A high standard of RPE should be used in conjunction with on-tool extraction.

 

General ventilation
 

It is likely that where there is work involving the use of power tools some dust will escape into the general workroom unless the processes are enclosed. Addition of clean air into the workroom is the most effective way to reduce general build up of dust over the working day.

The following PPE should be provided to reduce exposures that cannot be controlled by other means.

 

PPE - RPE

 

Different respirators provide different levels of protection (check ‘assigned protection factors’).

Respirators should only be used to control exposure after all other controls are in place.

It may not always be possible to introduce some of the controls above e.g. water suppression or it may be that the controls introduced do not sufficiently reduce exposures e.g. for disc cutting and polishing even introducing water suppression and LEV controls exposures may be above the WEL. In these circumstances RPE and in some cases a high standard of RPE may be required in addition to the controls implemented. Where a high level of protection is required (e.g. for high residual risk and/or work of more than 1 hour duration) then only power assisted respirators or air fed breathing apparatus will be adequate and suitable. If negative pressure RPE is used it should be selected and face fit tested for the operator.

 

Personal protection [such as protective clothing and respirators] may be needed as an interim measure where engineering controls are being developed and/or modified and for short-term jobs such as cleaning, emptying waste receptacles and maintenance; personal protective equipment can only help the person who wears it. 

 

RPE is no substitute for effective control of dust at source.

 

Personal and work-related factors in selection of RPE.

 

All types of RPE restrict the wearer to some extent, by imposing extra breathing resistance on the lungs and by restricting visibility or mobility.  These restrictions underline the need to control exposures by other means wherever possible.  It is also important to remember that effective protection is only given when equipment which is of the right standard and in good condition is properly fitted and used.

 

Removal of the RPE, even for short periods, dramatically reduces the level of protection afforded to the wearer.

 

A respirator which is not worn or is hung around the neck gives no protection at all.

 

Face masks depend on good contact between the skin and mask for their effectiveness.  Many face masks are available in one size only and cannot be expected to fit all the working population.  A good fit and seal are essential – without them the respirator will not give effective protection.  It is advisable to obtain a selection of different models of RPE so that masks can be selected to give the best fit for individual wearers.  It will only be possible to get a good seal if the skin in the region of the seal is smooth and without hair.  Facial hair or glasses will tend to lift the mask off the face and permit inward leakage of contaminated air.  For face fitting instructions refer to Fit testing of respiratory protective equipment face pieces,  HSE 282/28 Jan 03. 

 

Training

 

Everyone who is involved in the use of RPE should be appropriately trained. They must be aware of why the RPE is being worn and how it should be worn properly. Training may be available from the supplier or manufacturer of your RPE.