Page 9 - PPE GUIDELINE

Guidelines on the Use of PPE Against Chemical Hazards

(3) For the purpose of this regulation, “degree of protection” means the ratio of the
airborne concentration of the contaminant outside the respirator to the
concentration of the contaminant inside the face piece of the respirator.

The degree of protection afforded by the personal protective equipment must be taken
into account when determining compliance with the permissible exposure limits. The
effectiveness (degree of protection) of a respirator is determined by its protection
factor (PR). In the selection of respirators, the assigned protection factors are used.
For adequate respiratory protection, select a respirator with an assigned protection
factor greater than or equal to the hazard ratio. The hazard ratio (HR) is the ratio of an
airborne contaminant to its permissible exposure limit.

For example, an employee wearing a respirator having an assigned protection factor
of 10 and whose average personal exposure to xylene is 350 parts per million is
considered to be exposed to 35 parts per million xylene during the period he is
wearing the respirator. If he only wears the respirator for certain number of hours out
of the eight-hour work shift, then his daily time-weighted exposure is calculated thus:

(C w t w + C nw t nw) / 8

where C w , t w = exposure concentration, duration while wearing respirator
C nw , t nw = exposure concentration, duration while not wearing respirator

A wearing of the respirator for four hours in the above situation will result in a daily
time-weighted exposure of ((35 x 4) + (350 x 4)) / 8 = 192.5 parts per million xylene,
which is non-compliance since the permissible exposure limits of xylene is 100 parts
per million.

NB: Please refer to Section 3.2.3 for further discussion on ‘assigned protection
factor’.

Department of Occupational Safety & Health, Ministry of Human Resources, Malaysia ™October 2005 9