Introduction to Health and Safety at Work

exhaust duct
– this exhausts the air to the outside 
of the building. It should be checked regularly to 
ensure that the correct volume of air is leaving the 
system and that there are no leakages. The exhaust 
duct should also be checked to ensure that there is 
no corrosion due to adverse weather conditions.
An Introduction to Local Exhaust Ventilation
, 
HSG 37, 
HSE Books
, is a very useful document on ventilation 
systems.
The COSHH Regulations require that such ventila-
tion systems must be inspected at least every 14 
months by a competent person to ensure that they are 
still operating effectively.
The effectiveness of a ventilation system will be 
reduced by damaged ducting, blocked or defective fi lters 
and poor fan performance. More common problems 
include the unauthorized extension of the system, poor 
initial design, poor maintenance, incorrect adjustments 
and a lack of inspection or testing.
Routine maintenance should include repair of any 
damaged ducting, checking fi lters, examination of the fan 
blades to ensure that there has been no dust accumula-
tion, tightening all drive belts and a general lubrication of 
moving parts.
The local exhaust ventilation system will have an 
affect on the outside environment in the form of noise 
and odour. Both these problems can be reduced by 
regular routine maintenance of the fan and fi lter. The 
waste material from the fi lter may be hazardous and 
require the special disposal arrangements described 
later in the chapter (14.14.3)
Dilution (or general) ventilation
Dilution (or general) ventilation uses either natural ven-
tilation (doors and windows) or fan-assisted forced 
Figure 14.9
Typical local exhaust and ventilation system.

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