Introduction to Health and Safety at Work

13.9 
Dangerous substances
13.9.1 Introduction
The Dangerous Substances and Explosive Atmosphere 
Regulations (DSEAR) applies at most workplaces where 
a dangerous substance is present or could be present.
The employer must:
➤
carry out a risk assessment of any work activities 
involving dangerous substances
➤
provide a way of eliminating or reducing risks as far 
as is reasonably practicable
➤
provide procedures and equipment to deal with 
accidents and emergencies
➤
provide training and information to employees
➤
classify places where explosive atmospheres may 
occur into zones and mark the zones where neces-
sary. ( This duty is being phased in see table on page 
9 of 
Fire and explosion how safe is your workplace?
DSEAR)
The Regulations give a detailed defi nition of ‘danger-
ous substance’, which should be referred to for more 
information. They include any substance or preparation 
which, because of its properties or the way it is used, 
could be harmful because of fi res and explosions. The 
list includes petrol, liquefi 
ed petroleum gas (LPG), 
paints, varnishes, solvents and some dusts. These are 
dusts which, when mixed with air, can cause an explo-
sive atmosphere. Dusts from milling and sanding oper-
ations are examples of this. Most workplaces contain a 
certain amount of dangerous substances.
An explosive atmosphere is an accumulation of 
gas, mist, dust or vapour, mixed with air, which has the 
potential to catch fi re or explode. Although an explosive 
atmosphere does not always result in an explosion 
(detonation), if it catches fi re, fl ames can quickly travel 
through the workplace. In a confi ned space (e.g. in plant 
or equipment) the rapid spread of the fl ame front or rise 
in pressure can itself cause an explosion and rupture of 
the plant and/or building. For a detailed summary of the 
Regulations see Chapter 17.