HVAC System Sampling and Cleaning in Mold Remediation Projects

May 19, 2004
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courtesy of Abatement Technologies


courtesy of Abatement Technologies
Q: I have recently been involved in several mold remediation projects. It is not clear to me when the HVAC system does and does not require sampling, and when during the process of remediation I should have the system cleaned.

A:With respect to sampling the HVAC system, the suggestions in the Institute of Inspection, Cleaning and Restoration Certification's S520 Standard and Reference Guide for Professional Mold Remediation are highly relevant. The S520 highly recommends an initial inspection by the remediator, with the goal of making a preliminary determination of "areas of moisture intrusion and actual or potential mold growth." This information can then be used to determine whether further assessment by an Indoor Environmental Professional (IEP) is needed.

The S520 incorporates, by reference, the National Air Duct Cleaning Association document "ACR 2002: Assessment, Cleaning & Restoration of HVAC Systems." It states, "If significant accumulations of contaminants or debris are visually observed within the HVAC system..." or "...if evidence of microbial growth is visually observed or confirmed by analytical methods, then cleaning is required."

In section 4.2.1, the S520 Standard makes the following comment: "...In circumstances where an entire building or system (such as an HVAC system) is fully involved as a result of Condition 3 mold contamination or when the scope of work can be determined without sampling or independent IEP inspection and assessment, engagement of an IEP for assessment may not be necessary."

If visible growth (Condition 3) is found in the system during the remediator's initial inspection, then the system will require appropriate remediation (cleaning or replacement of components) to return it to Condition 1 (normal fungal ecology). In this situation, assessment by an IEP is not necessary to determine whether or not to clean the system, although it may be appropriate to sample the remainder of the indoor environment to establish the extent of contamination and the complete scope of work.

The HVAC system is designed to control temperature and humidity by evenly distributing conditioned air throughout the structure. It is equally capable of distributing aerosolized contaminants throughout the environment, unless steps are taken to prevent this from occurring. If more than minimal growth is found in the system, a logical assumption can be made that it is likely that contaminants have spread to other parts of the building. The actual presence and extent of the spread of these contaminants cannot be determined without sampling by an IEP.

If your initial inspection does not indicate a mold problem in the HVAC system, you have several options.
1. You can assume the system is contaminated at Condition 2 (settled spores) and determine an appropriate scope of work to return it to Condition 1. Since this requires cleaning the entire system, you will not need the services of an IEP to pre-sample the HVAC system.
2. An IEP can be retained to determine whether or not the HVAC system is contaminated.
3. You can assume the system is not contaminated and proceed accordingly, with no remediation performed on the system.

The remediator's liability is limited with either of the first two choices, since any contamination of the system should be detected or remediated. If choosing option three, which assumes that the system is not contaminated and therefore no remediation will be performed on the system, the remediator may face increased liability.

Another consideration is that the remediator may not have the authority to make the decision to sample. Ultimately, the choice is made by the property owner or other interested parties who will be paying for the IEP's services. The remediator's influence is often limited to making a recommendation as to whether he or she believes sampling is appropriate. If there is contamination and sampling is not performed, the responsible party may save money; however, the remediator may unknowingly assume much of the resultant risk.

In the S520 there is a Standard section and a Reference Guide chapter on Limitations, Complexities, Complications and Conflicts. This information was included to give the remediator some guidance in handling awkward situations. Regardless of the circumstances, it is up to the remediator to use professional judgment and make the final decision as to whether he or she is willing to accept a scope of work that may create a problem or disagreement.

HVAC System Cleaning
The options as to when to clean the system can be reduced to three scenarios:

  • Before the process of structural remediation begins.
  • After post remediation verification has confirmed that the structure has been returned to Condition 1.
  • At some point during the structural remediation process.

    Each approach has inherent consequences. Cleaning before remediation increases the likelihood that the remediation will not be effective, for two very simple reasons.

  • Most HVAC cleaning processes put the duct system under high negative pressure.
  • Most HVAC systems leak significantly.

    When cleaning is attempted before remediation, it is possible that the system will be continuously re-contaminated from drawing in contaminants from the surrounding, still-contaminated structure.

    Additionally, if the interior of the structure is contaminated, then those cleaning the HVAC system are working in a contaminated environment. This requires appropriate engineering controls and personal protective equipment. The net result is added cost and slower production times.

    When cleaning is attempted after remediation has been completed and return of the structure to Condition 1 has been documented, this means the structure surrounding the system has been returned to a normal fungal ecology. When the system is put under high negative pressure as part of the cleaning process, the air that is pulled through the system is to be less likely to be contaminated, so the cleaning process is more likely to be successful.

    There are two potential drawbacks to cleaning the system after the building has been remediated:

  • If improperly performed, cleaning the system can result in cross-contamination of the structure.
  • If the structure has been sampled to verify its return to Condition 1 prior to the cleaning of the system, an additional round of sampling would be needed after system cleaning to verify that cross-contamination did not occur. This means additional costs and delay, which customers may not tolerate. However, if the cleaning of the system is being subcontracted, this may be the only way to determine who is responsible for any cross-contamination that occurs.

    If you decide to clean at some point during the structural remediation process, the logical time to perform HVAC system cleaning frequently would be near the end of the detailed cleaning process. The chance of significant cross-contamination from the structure to the system is likely to have been significantly reduced. At the same time, the consequences of discharge of contaminants from the system into the structure are less, since one or more rounds of detailed structure cleaning remain to be performed, collecting any accidentally released contaminants. This timing is probably best if your company is performing the HVAC cleaning in-house.

    Making good decisions with regard to sampling and cleaning an HVAC system that is known or suspected to be contaminated requires knowledge of relevant industry standards combined with common sense and good professional judgment.

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