Introduction to Fire Safety Management

Introduction to Fire Safety Management
132
In order to prevent the formation of an explosive 
atmosphere from the dispersion of dust in air or by 
equipment, it is appropriate to design conveying and 
removal systems to an approved standard. Such 
equipment will remove the levels of dust within the 
enclosure which will help to avoid primary explosions; 
however, secondary explosions could still easily occur if 
the lying dust is suffi ciently agitated leading to entrain-
ment in the conveying and removal systems.
The avoidance of ignition sources that may precipi-
tate an explosion for either gas or dust in the atmosphere 
provides a relatively good control measure; however, in 
relation to dusts, accumulations and moisture content 
must be managed effectively as together they have the 
potential for self-heating and therefore self-ignition, thus 
the management of temperature and moisture in relation 
to dust must be considered.
Mechanical inputs can also produce either glowing 
sparks or hot spots and while the sparks are not 
suffi ciently energetic to provide ignition repeated contact 
may run the risk of igniting a dust cloud.
The removal of any foreign objects from process 
streams and the use of non-sparking or spark-proof 
equipment (intrinsically safe) must be considered in 
either gaseous or dusty atmospheres.
Ensuring that any electrical equipment is subject to 
regular maintenance (planned preventive maintenance) 
must also be seen as a key area to prevent ignition 
sources initiating an explosion.
Electrostatic sparks from static electricity must also 
be minimised and the following should be considered:
➤
The use of conducting materials for equipment, 
plant, etc. to avoid charge build-up
➤
The earthing of any equipment that may become 
charged
➤
The earthing of workers
➤
Earth non-conducting materials via an earth rod 
through the storage vessel.
With regard to electrostatic discharges if there is any 
doubt earthing should take place.
Mitigation
In relation to dust the best way to contain a primary 
explosion is to ensure that the process equipment is 
strong enough to withstand it. Dust explosion pres-
sures are usually within range of 5–12 bars. Designing 
the plant as though it were a pressure vessel is likely 
to cause it to be very expensive and beyond what is 
reasonably practicable. It is therefore quite often that 
designers will resort to explosion venting.