Harnessing Air When Building Containment
When starting a mold job that requires building containment, stop for a few minutes and think how the containment will be built. It can have a positive impact in reducing the costs of the job.
Planning for how the work is going to be accomplished inside containment and then building containment that “compliments” the job site and the work to be accomplished is beneficial. Numerous materials and configurations can be used to build effective containment.
After deciding where the containment is going to be built, the next decision is what kind of materials are going to be utilized to build the required framing. I personally prefer the use of PVC tubing, which is low cost, is strong if purchased in an appropriate diameter (at least 1 inch), absorbs nothing and can be reused on future jobs.
Other mold remediators prefer to use framing lumber and/or spring poles. All these materials will work, and if assembled properly, will do the job of holding up the containment under negative air pressure for the duration of a mold remediation job.
Just as there are multiple framing materials, there are multiple ways to create an entrance or exit. The most common are: A zipper opening (single or double zipper), a “T” flap or a “Z” flap.
Again, I have a preference, which is the “Z” flap. My opinion is based on field experience; I have had zippers fail, and a “T” flap will not prevent potential contamination “leakage” from coming out of containment in the event that a negative air machine (NAM) either fails, blows a circuit breaker, or is turned off or unplugged.
Measurements can verify both that the containment is “tight” enough and has adequate air flow. Tightness is a measurement of the vacuum, or pressure difference, from inside and outside containment. This pressure differential is measured in either metric units (pascals, abbreviated Pa) or in English units (inches of either water column or mercury column). I prefer just going with the metric units.
The second measurement is what is called ACH (air changes per hour). Most mold jobs will be sized (the negative air machine) to move four air changes per hour.
This calculation is straight forward: Volume of air inside containment multiplied by the air changes per hour (usually four), which gives cubic feet of air per hour. This is then divided by 60 (minutes/hour) to convert to cubic feet per minute, which is the measurement of airflow through an air filtration device:
Cubic feet x air changes per hour ?? 60 = CFM required
The next step is to actually build the containment, which can be as simple as covering a doorway into a small bathroom that is to function as the work site. Often, containment can be quite large, involving many rooms, sub-divisions of large rooms and separate rooms each being its own worksite/chamber.
When the poly sheeting is being put together, think of it as wrapping a large present. The joints or connections of the sheeting need to be secured together. There are two methods of attaching the sheeting together: Tape and/or spray adhesive. While tape appears to be simpler, spray adhesive is actually stronger in that it chemically bonds the poly sheeting together.
Proper containment set up saves time and money
Once the containment has been built, the next step is where some of the initial planning can have a significant impact on cost. Typically, the volume of airflow from the air filtration device is too large for the contained area, resulting in too much negative pressure.
The way to reduce the pressure difference is by cutting “vents” in the containment to allow for adequate air flow. This will lower the negative pressure back to the range of 5 Pa. Where these vents are placed can have a significant impact on cost.
For clearer detail on the concept of using airflow to aid in cleaning, let’s look at the included images. Both are of the same containment, but Image B is the superior way to set up containment.
In Image A, the containment has a vent cut in the wall near the entrance/exit door. The blue path through the containment shows how the air entering containment will flow toward the negative air machine. In this vent set up, the air flows through the center of containment and does not get near the work area.
In Image B, the vent is cut at the opposite end of the work area, from the negative air machine. As the air enters, it travels directly across the “dirty area” and into the negative air machine (see the blue path). Thus, the air’s path acts as a cleaning mechanism, as it will carry airborne particles from the work area directly into the negative air machine.
This process of controlling how the air flows will reduce the amount of debris that gets into the air inside containment, and thus reduce the amount of labor required for detailed cleaning. Additionally, the cleaning work should be performed from the vent toward the negative air machine so the airflow will flow across the dirty area and into the negative air machine — left to right in this case.
Controlling where the air flows inside a properly built containment can help reduce the labor content in the cleaning process, which will have a positive impact on your profitability.
Richard Driscoll has a B.S. in mechanical engineering from Clarkson College of Technology, an MBA from the University of Dayton and is currently working on his doctorate. He is a professor at Webster University where he provides graduate and undergraduate level lectures. He is an IICRC Certified Master Restorer, Master Textile Cleaner and an approved instructor. Driscoll has been consulted by state governments on legislation related to the cleaning and restoration industry. He also is the author and instructor for Restoration Sciences Academy’s MR-110 and MR-210 microbial remediation classes and MR-211 trauma scene clean up class. He can be reached at [email protected].