JSP 375 Vol 2 

MoD Health & Safety Handbook 

4.2 

Modifying the process to eliminate production of a hazardous by product or waste product. 

4.3 

Substituting the hazardous substance by a new substance which presents no risk or less 

risk to health. 

5 

Examples of prevention/substitution include: asbestos replaced by MMMF; shot blasting using inert 

materials rather than sand; mercury gauges replaced by mechanical pressure gauges; detergent 

solutions for cleaning instead of organic solvents; water based paints and adhesives rather than those 

based on organic solvents; riveting instead of welding; using sealed batteries instead of ones requiring 

topping up with acid. 

6 

Care should be taken that any proposed new process does not introduce new risks   or if it does, 

that these are less than the original and more easily controlled. 

7 

Reference should be made to project sponsors as appropriate when attempting to identify suitable 

alternative processes or substances.  If necessary, feedback should be raised (e.g. in the form of a 

 defect acquaint ). 

LEVEL OF CONTROL OF EXPOSURE 

8 

If it is not reasonably practicable to prevent exposure to hazardous substances, then it should be 

controlled to within the appropriate occupational exposure limits (OELs) published in EH40 (and updated 

annually) by the Health and Safety Executive (HSE).  Compliance with these limits demonstrates 

adequate control of exposure by inhalation as required by the COSHH Regulations.  The absence of a 

limit does not mean that the substance is harmless. 

9 

There are 2 types of OELs; maximum exposure limits (MELs) and occupational exposure 

standards (OESs).  Both types of limit are concentrations of hazardous substances in the air, averaged 

over a specified period of time referred to as a time weighted average (TWA). 

Maximum Exposure Limits (MEL) 

10  A MEL is set for substances which may cause the most serious health effects, such as cancer and 

occupational asthma, and for which  safe  levels of exposure cannot be determined, or for substances 

for which safe levels may exist but control to those levels is not reasonably practicable.  Exposure 

should be reduced as far below the MEL as reasonably practicable and should not exceed the MEL 

when averaged over the specified reference period.  For substances given a short term MEL (15 minute 

reference period), this level of exposure, averaged over the reference period, should never be 

exceeded. 

Occupational Exposure Standards (OES) 

11  An OES is set at a level at which there is currently no indication of risk to the health of workers 

exposed by inhalation day after day.  Exposure to a substance with an OES should be reduced to no 

higher than that level; if the OES is exceeded, the reason must be identified and measures must be 

taken to reduce exposure to the OES as soon as is reasonably practicable. 

`Sk' Notation 

12  Some substances can pass through the skin, enter the blood stream and cause harm elsewhere in 

the body.  Substances for which this effect could be significant are given the  Sk  notation in EH40, 

indicating that particular care must be taken to prevent skin contact with them. 

Leaflet 5 Annex G 

Page 2 

 April 

2003