Published On: July 1, 2024

Why should I go to the expense of buying a manometer to measure negative pressure? If my plastic is sucking in, that is proof enough that my containment is under negative air!

The primary liability for a mold remediation contractor is cross contamination from a failure in containment. Failure can result from poor construction, not using an exit/decon chamber, improper doffing of PPE, poor cleaning techniques and not maintaining adequate pressure differentials. When I ask most restorers how they determine if they have created negative pressure inside containment, the most common answer I get is “Well of course!! If my plastic is pulling in, we have plenty of negative air!” But the reality is, even though it may appear that there is a dramatic pull on the plastic, it Is not even close to the minimum pressure needed. The only way to know the true amount of negative pressure that is being created and maintained is to use a manometer. The ANSI/IICRC S520 states the minimum negative pressure that should be maintained to prevent contaminants from leaving a contained area is -5 Pascals (Pa) or -0.02 inches of water column. For those of you that have never used a manometer to visually see what -5 Pascals looks like compared to being measured on a manometer, it is A LOT of negative air! The containment that is constructed must be built to withstand that amount of negative pressure and withstand the amount of worker activity for the duration of the project. Containments are not constructed to be airtight. It is not practical or possible with the common materials we use to construct containment from. Plus, make-up air must be able to enter the containment to allow for the necessary number of air changes.

There will be some loss in pressure upon entry and exit so realistically, it is better to maintain a negative pressure between -8 to -10 Pa to allow for some flexibility in pressure changes yet prevent it from dropping below the minimum desired pressure of -5 Pa. It is a good idea once containment is built to test the pressure by entering into the containment while monitoring the pressure using a manometer. I use the goal that my containment should not lose more than 0.5 Pa upon entry and exit. It there is a loss of pressure of up to 1 Pa, it is still acceptable but any more than that and I would be looking for breaches in the construction and make the necessary repairs to prevent excessive pressure loss.

Some manometers can provide data logging options for documentation that can reduce liability for the contractor. Some units may also provide options for notifying the restorer after hours via wireless cellular plans to notify the restorer in the event of a loss in pressure. These manometers are typically expensive but can also be billed to the project as remote monitoring. Great examples of high caliber manometers are the Omniguard 5 and Abatement Technology RPM-RT Series. There are other less expensive handheld manometers that can be used to measure and document containment pressures that may not have all of the bells and whistles but provide the restorer with the needed confirmation of the pressures that have been established and can be manually recorded for documentation purposes. Extech and Dwyer offer handheld options that have digital displays and have the ability to store the data and also connect to a computer to allow the data to be downloaded into a hard copy format. Additionally, there are even less expensive options, but the quality and accuracy go down significantly.

It is also possible to create too much negative pressure which can result in collapse of the containment, backdrafting, flame rollout and drawing unwanted moisture or contaminants from unwanted areas. Backdrafting occurs when the negative air is strong enough that carbon monoxide is pulled into the containment from an exhaust flu of a furnace resulting in oxygen deficient atmospheric conditions. Flame rollout can occur when negative air pressure is strong enough to pull natural gas from gas appliances resulting in explosive atmospheres.

Measuring and monitoring negative pressure allows the restorer to ensure the engineering controls they have put in place adequately prevent cross contamination from occurring which will also reduce liability and allow for a successful outcome for the overall project!

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