Mold Therapy: Negative Air Containment A Key to Successful Mold Remediation

February 1, 2002
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There is probably no subject that has received more attention in the restoration industry in the past year than that of mold and the health effects of mold exposure. This topic has not just been isolated to the restoration arena.

The disaster restoration industry is no exception.

Mold-related problems have also caught the attention of many in the legal community who are beginning to view mold as "the next asbestos." Every professional cleaner coming in contact with mold-contaminated structures should both understand the proper procedures and techniques used in remediation, and the techniques used to avoid contaminating the structure further by releasing additional mold spores as well. This is critical in protecting employees from the potential health effects of mold and their businesses from the possible cost effects of litigation.

Three terms that continually arise in discussions and in protocols for mold remediation are: "containment," "negative air" and "air changes per hour." These different terms are interrelated and involve the use of air scrubbers or negative air machines. I will attempt to describe and define each of these terms and how they relate to a typical mold remediation job.

Negative Air Containment Principles
Containment is the process of isolating a contaminated area from the rest of the facility. This is nothing new. For years, restoration contractors have used common sense and hung a piece of poly or a tarp over a doorway to prevent the spread of contaminants from one area to another. Today the process is a little more sophisticated, but the end goal is the same -- to prevent the contaminants from spreading.

Negative pressure can be described as a partial vacuum and can be demonstrated with the use of a drinking straw. Sucking on one end of a straw creates a negative pressure zone inside the straw. Air flows into the opposite end of the straw due to the negative pressure inside the straw. This pressure differential is maintained as long as more air is removed from the straw than can be replaced. Containment areas under negative pressure behave in the same way, as lower pressure inside the containment pulls outside air in and prevents the contaminated air from escaping.

There are basically two types of containment: Source containment and full-area containment. Severity of the mold growth and the size of the contaminated area will generally dictate which type of containment to use.

Local Containment Procedures
When the contaminated area is small and easy to dispose of without causing further contamination, simple source containment may be an option. Negative pressure is generally not used during this type of operation. Removing a moldy ceiling tile and sealing it in a plastic bag is a good example of a source containment application. This method should only be used when there is no chance that any appreciable number of mold spores will be released while the contaminated object is being removed and bagged.

Source containment can also be used with localized negative pressure if a very small area with mold must be removed. A one-square foot patch of mold on a wall would be an example. A small piece of poly can be taped around the area to be removed. A small HEPA vacuum can be used for this purpose by inserting the inlet nozzle inside this small containment to create a negative pressure and to vacuum up released particles.

Full Containment Procedures
Full containment is used when the contaminated area is larger or requires some invasive activities to remove the mold source. In full containment the entire containment area must be kept under negative pressure at all times during the mold abatement process to prevent the escape of any air that could potentially contaminate other parts of the facility. An example of this type of containment would be the removal of mold-contaminated wallboard.

If the contaminated area is small, an enclosure of polyethylene sheeting is typically constructed that is large enough to completely cover the work area and to accommodate a worker. The poly can be taped, glued or tacked to the wall area around the portion that is being removed to form one side of the containment. Adjustable poles or similar devices can be used to form the other three sides.

When the structure is complete it should look like a large shower or a tent made of poly, with a double flap door to allow entry without losing negative pressure. If the structure is built properly, it will be almost airtight around the perimeter and will allow make up air to enter through the door opening.

If the contaminated area is larger a full-scale containment area must be erected. Poly is applied to cover all the walls, floor, and ceiling of the area under containment. It may be necessary to also construct airlocks, pass-throughs and equipment rooms, depending on the work that must be done and the equipment required.

Full containment always requires that negative pressure be maintained inside of the containment area. The purpose of the negative pressure is to ensure that any directional air movement is from the clean air environment into the contained area, and not the other way around. This ensures that contaminated air from inside the containment will not flow out through doors, openings, cracks, etc. into the clean area.

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