HOW TO DECIDE IF A RESPIRATORY PROTECTIVE DEVICE IS BOTH SUITABLE AND ADEQUATE FOR A GIVEN APPLICATION

A         SUITABILITY

A device is suitable if it provides appropriate protection for a given application.  To do this it must:

i.             Fit the person to whom it is issued, taking into account for instance whether they  have beard,spectacles etc.

ii.            Br capable of providing the appropriate protection (e.g. fitted with correct filters, of be to the appropriate standard etc).

iii.           Be matched to the task, e.g. not hinder mobility or vision unduly, not impose undue physiological burden (particularly relevant for wearers with medical conditions, some of whom may not be capable of safely wearing RPE). The wearer must be capable of doing their job with minimum impedance from the device  worn.

iv.           Be compatible with any other items of PPE worn, e.g. eye, face, hearing or skin protection,  and not degrade the protection offered by any of these devices.

v.            Be not likely to cause or exacerbate heat strain - this is a significant risk where  protective clothing is used in combination with respiratory protection.

vi.           Give sufficient duration for the application.

B         ADEQUACY

A Respiratory Protective Device is adequate if it provides a sufficient level of protection to reduce the exposure of the wearer to an acceptable  level.  To determine this, it is necessary to know the expected concentration of contaminant in the workplace, and calculate the minimum factor by which it must be reduced to reach an acceptable level.

It would be a matter of assessment in any given situation what constituted an acceptable level, but in any case this must be well below any applicable Exposure Limit (e.g. OES, MEL, MAK, TLV).

This minimum factor defines the minimum required Protection Factor of the RPE.  Protection Factor is defined as:

               PF =  Contaminant Concentration Outside The Mask
                         Contaminant Concentration Inside The Mask

The Protection Factor of any given device is very much dependent on the level of leakage.  Leakage can vary greatly depending on fit, flow rate (if applicable), training and motivation of wearer, temperature and humidity, application and many other influences.  Historically a Nominal Protection Factor (NPF) has been quoted for a given class of respirator, this being  based on the minimum acceptable performance in laboratory tests.

It was thought that, since the laboratory tests were designed to provide a realistic assessment of the respirator leakage on actual human test subjects, and  the number quoted was based on the minimum allowed performance, the NPF was a realistic indicator of workplace performance. More recently however, an increasing number of Workplace Protection Factor (WPF) Studies, carried out  in real workplace situations, have indicated that in many cases this is not a realistic approach.  Instead a new system will be adopted in the UK, whereby more realistic Assigned Protection Factors will be set.  These APF's, contained in the revised standard BS4275, allow safety professionals to make a much safer assumption about the level of protection offered by a respirator.

It should be noted that standards are frequently reviewed and the above information is subject to change.  If in doubt, check the latest draft of the  appropriate standard.

The Assigned Protection Factors given overleaf are those which will be used in the United Kingdom.  The approach is a cautious one, and it would therefore seem appropriate that users outside the UK follow these guidelines also.  There are, however, different Assigned Protection Factors published in Germany - ZH1/701 - Regeln fu`` den Einsatz von Atemschutzgera``ten by HVBG, and by OSHA in the United States.

In all cases, to decide if a given respirator is adequate:

Minimum required APF =            Workplace Concentration
                                           Maximum Acceptable Exposure Concentration