Page 241 - IGC BOOK

to a safe place. This will usually be into the atmosphere and care must be taken to ensure that
this does not create an atmospheric pollution problem; factors such as chimney height and
prevailing wind direction and speed must be considered to ensure adequate dispersal. The
efficiency of the exhaust outlet must not be impaired by variations in wind direction or by
weather cowls (which should be sited well away from the end of the duct). Exhausted air must
also be directed away from any air inlets, otherwise a cyclic pollution system is produced.

Effectiveness of a LEV system will be reduced by:
• Poorly positioned intake hoods.
• Damaged ducts.
• Excessive amounts of contamination.
• Ineffective fan due to low speed or lack of maintenance.
• Blocked filters.
• Build-up of contaminant in the ducts.
• Sharp bends in ducts.
• Unauthorized additions to the system.

Inspection and Monitoring

LEV systems should be routinely inspected and maintained to ensure their ongoing effectiveness,
through:

• Routine visual inspection – to check the integrity of the system, signs of obvious damage
and build-up of contaminant, both outside and inside the ductwork; filters should be
visually inspected to ensure they are not blocked; the exhaust out-feed should be checked.

• Regular visual inspections, either as part of daily operations or as a more formal
procedure perhaps involving specific checks, are often a first indication that there is a

problem. A typical example might be where a local exhaust ventilation system is in place
to remove sawdust generated by a circular saw. An excessive build-up of sawdust around
the saw might indicate a problem with the system.

• All hoods should be examined in detail to ensure they capture or contain the contaminant
effectively. This may be done by using smoke generation to follow the airflows around a
hood or by taking airflow measurements.

• Manometers (pressure gauges) or U-tubes can be used to measure static pressures at
hoods or enclosures. They can also be used to measure pressure drops across filters or air
cleaning plant. The measurements will confirm the suitability of airflow distribution and
agreement with the design specification.

ENSIGN| Unit IG2 – Element 7 – Chemical and Biological 36
Agents