Introduction to Health and Safety at Work

Introduction to Health and Safety at Work
238
ventilation system to ventilate the whole working room 
by inducing a fl ow of clean air, using extraction fans fi t-
ted into the walls and the roof, sometimes assisted by 
inlet fans. It operates by either removing the contaminant 
or reducing its concentration to an acceptable level. It is 
used either when airborne contaminants are of low tox-
icity, low concentration and low vapour density or con-
tamination occurs uniformly across the workroom. Paint 
spraying operations often use this form of ventilation as 
does the glass reinforced plastics (GRP) boat-building 
industry – these being instances where there are not dis-
crete points of release of the hazardous substances. It 
is also widely used in kitchens and bathrooms. It is not 
suitable for dust extraction and where it is reasonably 
practicable to reduce levels by other means.
There are limitations to the use of dilution ventila-
tion. Certain areas of the work room (e.g. corners and 
beside cupboards) will not receive the ventilated air 
and a build-up of hazardous substances occurs. These 
areas are known as ‘dead areas’. The fl ow patterns are 
also signifi cantly affected by doors and windows being 
opened or the rearrangement of furniture or equipment.
14.9.5 Supervisory or people controls
Many of the supervisory controls required for COSHH 
purposes are part of a good safety culture and were dis-
cussed in detail in Chapter 4. These include items such as 
systems of work, arrangements and procedures, effective 
communications and training. Additional controls when 
hazardous substances are involved are as follows:
➤
reduced time exposure – thus ensuring that work-
ers have breaks in their exposure periods. The use 
of this method of control depends very much on the 
nature of the hazardous substance and its short-
term exposure limit (STEL)
➤
reduced number of workers exposed – only per-
sons essential to the process should be allowed in 
the vicinity of the hazardous substance. Walkways 
and other traffi c routes should avoid any area where 
hazardous substances are in use
➤
eating, drinking and smoking must be prohibited in 
areas where hazardous substances are in use
➤
any special rules, such as the use of personal pro-
tective equipment, must be strictly enforced.