Quantcast Establishing Negative Pressure

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ITG FY03-4
5 June 2003
Minimize seams in the sheeting material to reduce the possibility of
accidental rips and tears in the adhesive or connections. Overlap and stagger all
seams in the sheeting. Do not locate seams at corners or wall-to-floor joints.
Each enclosure consists of a work area, a decontamination area,
and waste storage area. Separate the work area where the mold removal
operations occur from both the waste storage area and the contamination control
area by physical curtains, doors, and/or airflow patterns that force any airborne
contamination back into the work area.
Construct the decontamination room or airlock for entry into and
exit from the remediation area. The entryways to the airlock from the outside and
from the airlock to the main containment area should consist of a slit entry with
covering flaps on the outside surface of each slit entry. The chamber should be
large enough to hold a waste container and allow a person to put on and remove
PPE. Place all contaminated PPE, except respirators, in a sealed bag while in
this chamber.
Establishing Negative Pressure. Air is to be drawn into the
enclosure under all anticipated conditions and exhausted through a HEPA filter
for the duration of the project. This can be accomplished through the use of
HEPA filtered fans exhausted to the outside of the building. For small, easily
contained areas, this can be accomplished using a fan or HEPA vacuum.
Check airflow patterns before removal operations begin and any
time there is a question regarding the integrity of the enclosure. The primary
tests for airflow trace air currents with smoke tubes or other visual methods.
Make flow checks at each opening and at each doorway to demonstrate that air
is being drawn into the enclosure and at each worker's position to show that air is
being drawn away from the breathing zone.
After the initial airflow patterns have been checked, monitor the
static pressure within the enclosure, using manometers, pressure gauges, or
combinations of these devices.
The design parameters for static pressure differentials between the
inside and outside of enclosures typically range from 5 to 25 Pa (0.02 to 0.10
inches of water gauge,) depending on conditions. All zones inside the enclosure
should have less pressure than the ambient pressure outside of the enclosure
e.g. -5 Pa (-0.02 inches water gauge differential). Design specifications for the
differential vary according to the size, configuration, and shape of the enclosure
as well as ambient and mechanical air pressure conditions around the enclosure.
The airflow volume (cubic meters per minute) exhausted (removed)
from the workplace must exceed the amount of makeup air supplied to the
enclosure. Design the rate of air exhausted from the enclosure to maintain a
negative pressure in the enclosure and air movement past each worker. The


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