Introduction to Fire Safety Management
Introduction to Fire Safety Management
Introduction to Fire Safety Management
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Ventilation of s<strong>to</strong>rage areas<br />
Ventilation has been discussed as part of the s<strong>to</strong>rage<br />
requirements; however, all areas where fl ammable liquids<br />
are handled should be adequately ventilated <strong>to</strong> ensure<br />
that any released vapours are diluted <strong>to</strong> a safe level.<br />
Whichever ventilation system is used it needs <strong>to</strong><br />
be capable of providing a minimum of six complete<br />
air changes per hour. The system’s capacity should<br />
ensure that the amount of vapour in the atmosphere is<br />
not only diluted <strong>to</strong> well below its fl ammable limit, but<br />
also reduced <strong>to</strong> a level below any relevant workplace<br />
exposure limit (HSE’s guidance note EH 40 gives advice<br />
on workplace exposure limits).<br />
Dependent upon the concentrations and volumes<br />
in use good, natural, well-positioned ventilation may be<br />
adequate, but where this cannot be achieved, mechanical<br />
ventilation and/or local exhaust ventilation (LEV) is<br />
almost certain <strong>to</strong> be needed.<br />
Positive pressure mechanical systems can be<br />
used <strong>to</strong> force air in<strong>to</strong> an area; diluting and venting any<br />
potential build-up of fl ammable vapours. Any area<br />
provided with a positive pressure mechanical system<br />
will also need <strong>to</strong> be provided with suffi cient openings<br />
<strong>to</strong> release the atmosphere created. LEV systems are<br />
designed <strong>to</strong> capture airborne contaminants such as<br />
fl ammable vapours, fi lter them and ventilate outside a<br />
building <strong>to</strong> a place of safety in the open air.<br />
Any vents provided for the release of pressure or<br />
contaminants should be a minimum of 3 m above ground<br />
level, at least 3 m from building openings, boundaries<br />
and sources of ignition, and away from building eaves<br />
and other obstructions where they could become<br />
trapped. The ducting taking the fl ammable vapours<br />
away should be arranged so that they cannot condense<br />
and collect at low points within them.<br />
Wind<br />
direction<br />
Causes and prevention of fi re<br />
Ventilation/fume cupboards – in certain operations<br />
(e.g. solvent-based spraying operations or decanting<br />
of fl ammable liquids) booths or cabinets are required<br />
<strong>to</strong> control the build-up of fl ammable vapours. In such<br />
instances the airfl ow rate in<strong>to</strong> all openings in the<br />
enclosure should be suffi cient (about 1 m/s) <strong>to</strong> prevent<br />
vapours entering the work area. These ventilation booths,<br />
cabinets and other enclosed equipment are generally<br />
designed <strong>to</strong> ensure that the vapours are kept below 25%<br />
of their LEL.<br />
As the outcome or failure of any ventilation system<br />
or part of the system may result in a build-up in vapour<br />
concentrations with the potential for both fi re and<br />
explosion, the system must be provided with an alarm<br />
system <strong>to</strong> provide warning.<br />
There are also a number of s<strong>to</strong>rage systems that<br />
are combined with booths and cabinets which use LEV<br />
for vapour control. Regardless of the system used each<br />
must be subject <strong>to</strong> rigorous maintenance testing and<br />
examination regimes <strong>to</strong> ensure that fl ammable vapours<br />
are controlled.<br />
Any electrical system used as part of the ventilation<br />
or extraction systems must meet rigid electrical<br />
standards and as in the case of all such equipment<br />
be intrinsically safe. As discussed earlier, classifying<br />
hazardous or potentially explosive atmospheres is not<br />
only a legal requirement under DSEAR but has been<br />
widely used <strong>to</strong> determine the extent of hazardous zones<br />
created by fl ammable concentrations of vapours.<br />
Over recent years the process of classifying hazardous<br />
areas in such a way has been extended from its<br />
initial purpose of selecting fi xed electrical equipment<br />
for use in the area, <strong>to</strong> helping <strong>to</strong> identify and eliminate<br />
potential ignition sources, including portable electrical<br />
equipment, vehicles, hot surfaces, etc. from fl ammable<br />
atmospheres.<br />
Figure 8.22 The use of wall and roof vents <strong>to</strong>gether, give<br />
good natural ventilation Figure 8.23 Example of a fume cupboard<br />
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