Post-Remediation Verification and Clearance Testing for Mold and Bacteria

Chapter 1

What is Post-Remediation Verification (PRV) ?

There are many common misconceptions about post-remediation verification (PRV) for mold and bacteria remediation projects. Some people think PRV is either air testing or surface testing.   Other people only perform a visual inspection (or possibly a "white glove" test) as their method of PRV. Still others think PRV is not necessary at all.

Post-remediation verification is actually a process that involves many steps . PRV will be a much less powerful tool if it is simply viewed as one step at the end of the process.   PRV should begin with the planning stages of a remediation project, follow through the remediation process, and then, sometimes conclude with a quality control check at the end of the project. This quality control check could consist of air testing, surface testing, or other types of testing. This entire effort is referred to as "process control."   Process control is the basis of quality control programs utilized in many different types of industries.   Verifying the quality of the product, in this case the remediated structure, requires documentation of the remediation process, not just the apparent end result . (See Chapter 6.)

The last part of PRV, the need for air testing or surface testing, commonly called "clearance testing" should vary, based upon the size and complexity of the remediation project. Similar to manufacturing quality control principles, the greater the volume of the items being produced and the more complex the items produced, the more quality-control steps are necessary.   The same parallels exist in mold/bacteria remediation projects.    The larger and more complex the microbial remediation project, the more detailed the quality control documentation of the process and/or PRV testing should be.  

A. Where Did the Concept of "Clearance Testing" Come From?

Clearance testing is a term that developed in the asbestos and lead abatement industries.   It basically was a combination of a visual inspection of the abated area and surface sampling (lead) or air sampling (asbestos) to insure that remaining levels of the substance in question were below a regulated level that was considered to be safe and/or acceptable. However, both of these industries also require or recommend confirmation of the use of proper work practices during the remediation project.

A parallel "clearance" or PRV concept has been suggested in many of the guidance documents for mold and bacteria r emediation.   In addition, we see an embracing of the use of air flow control technologies, a negative pressure containment, thorough cleaning, etc. for microbial remediation that are part of the quality control process in the lead and asbestos abatement industries.    Many of the safety and health professionals who now perform mold PRV are familiar with these concepts since a large number of them have previous experience in the asbestos and lead abatement industries.   These same people may also consider the concept of standard operating procedures (SOPs) (aka, quality control practices) used for lead and asbestos abatement to be appropriate for mold remediation as well. There are some technologies that do carry over well from the asbestos and lead abatement industries and some techniques that can spell disaster in the microbial arena.   Some of these differences will be discussed in this book and will hopefully help to augment the level of "professional judgment" of those practicing in this field.

B. Similarities Between Asbestos Abatement and Mold Remediation

It is interesting to note the evolutionary similarities between the mold and asbestos industries.

These are shown in the table on below:

Table 1 : Similarities Between Asbestos Abatement and Mold Remediation

Initial study by Selikoff-claiming serious health risks, later questioned. Initial hemosiderosis study-claiming serious health risks, later questioned.
Total asbestos sampling method - TEM (>0.3µ) 18 Total spore sampling method
Harmful fiber size method - PCM (>5 µ) (only >5 µ fibers cause disease) 17 Culturable spore sampling method (only viable spores can cause infection)
100 fibers per day (>5 µ) normal exposure background - minimal risk exposure level 4 4,224 spores/m 3 * average daily outside exposure level - generally effects only extremely sensitive individuals 33
Numerous regulations - since initial start of awareness in early 1970's in US. Regulations are just starting to be formulated 16
Media hype exaggerated health concerns Media hype exaggerated health concerns
Clearance of project done with aggressive air movement 18 Some IEPs do clearance air testing with aggressive air movement

* Mold is a complex mixture, unlike asbestos. High levels of one type, that can occur in damp and wet environments can cause problems while others appear innocuous.

C. Dissimilarities Between Lead Abatement and Mold Remediation

Lead abatement has few similarities to mold remediation.   The main similarity is the use of surface sampling to determine "clearance" of a mold remediation project.   However, mold and lead have numerous dissimilarities as shown in the table below:

Table 2 :   Dissimilarities Between Lead Abatement and Mold Remediation

Heavy particles fall out rapidly from the air during remediation Mold* spores, because of their small size, can stay airborne longer - aerodynamically more similar to asbestos fibers in size range
HEPA air filtering devices or AFDs (including NAMs and air scrubbers) not required HEPA AFDs are   essential for large scale projects to control dust and spores
Lead's major routes of exposure are ingestion and inhalation Mold's major route of exposure is inhalation* *
Lead does not have a normal atmospheric background level in all areas Mold spores are present virtually everywhere
Lead particles are not easily made airborne Mold spores are easily re-aerosolized by air currents, sporulation and other means

*Mold spores also include fungal fragments

**Certain molds are ingested in food products and can pose an ingestion hazard (for example:: Ergot from Fusarium ) when consumed in thousands to millions of spores.

D. How Mold/Bacteria Remediation PRV Differs from Asbestos and Lead Clearance Testing

The PRV concept for mold and bacteria remediation is similar to both asbestos and lead abatement clearance testing.    However, mold and bacteria remediation have their own unique set of circumstances and methodologies for assessing and measuring "clearance" that can go beyond a simple set of air or surface tests.   Hence the term PRV seems more all-encompassing and more appropriate.

One major difference between mold remediation and asbestos abatement i s the fact that a clearance air monitoring standard for asbestos fibers in the air has been defined in statutory regulations.   Such "acceptable-minimal risk" standards for mold do not exist in the United States at this time.    However, 30 other industrialized nations have defined   "normal" mold spore level standards.

The second major difference between mold, asbestos and lead clearance is that mold spores are found in significant concentrations in the normal everyday environment .   This is generally not true for asbestos or lead.   The relative scarcity of asbestos and lead in the natural environment allow for the use of "minimal detection" clearance standards.   That is, the clearance level is near the limit of detection for the sampling method.

If our purpose in mold remediation is to return an occupied space back to "normal" levels of a contaminant, then typical background levels play a major role in our definition of "cleanliness."   For some numerical comparisons, the background level of asbestos fibers in the air is typically 0.0001 f/ml (ATSDR 1991) .   On the other hand, it is common to find at least   0.01 mold spores/m 3 (10,000 spores/m 3 ) in the outside air in the summer time in temperate climates. This means that t ypical outdoor mold spores levels in the air are at least 100 times higher per cubic meter than they are for asbestos. As a result, for a typical mold remediation project, the term cleanliness is far less stringent than for an asbestos project.   An exception to this statement would occur when dealing with opportunistic pathogenic fungi, especially with susceptible populations.   In such cases, very stringent cleanliness levels are required.   (See Chapter 5 Section F)

Mold spore surface sampling is similar to lead surface sampling in that both methods look for remnants of what was supposed to have been removed.   However, there are also two reasons why surface sampling for mold is more significant than for lead.   First, remnants of mold growth may cause serious symptomatology in highly sensitive individuals.  Second, viable mold spores and hyphal fragments may predispose a building to accelerated mold growth in the future if another water intrusion occurs.  Also, since lead and asbestos are inorganic and do not grow, the clearance residuals from lead and asbestos are fixed quantities.  As for mold, the addition of water can result in more mold growth.

E.  The Use of HEPA-Filtered Equipment

Like asbestos and lead abatement, mold remediation projects can also generate large concentrations of airborne particles, especially when old building materials and wall cavities are disturbed.    Even in commercial buildings, the disturbance of suspended ceiling tiles has been shown to release significant quantities of airborne dust and mold spores. Clearly, the use of HEPA-equipped AFDs for dust control is necessary for large scale mold projects.   They may also have a role in smaller, more localized projects to control the spread of particulates.

As interesting question exists regarding the necessity of HEPA air filtration in mold remediation. Most mold spores are in the range of 2-5 microns.   At the extremes, some mold spores are as large as 120 microns, while some are as small as 0.3 microns.   A HEPA air filter is designed to remove particles that are 0.3 microns in size at an efficiency of 99.97%.   Interestingly, HEPAs are more efficient at both larger and smaller particle sizes.   More efficient capture of larger particles is fairly easy to understand but the more efficient capture of p articles smaller than 0.3 microns is not intuitive.   However, particle dynamics of very small particles is influenced as much by their temperature (kinetic energy) as by gravity.   Particles smaller than 0.3 microns floating around in the air at ambient temperatures behave much like a pinball in a pinball machine.   This erratic behavior gives the particle a greater probability of colliding with the HEPA filter media as it attempts to pass through it.

One might ask if a HEPA air filter necessary for a mold remediation job, when the particles are typically much larger than 0.3 microns.  To answer this question, we need to look at another dimension to the mold contamination issue.  This has to do with fungal fragments.   The issue of fungal fragments is also raised in S520 (See next chapter).  Fungal fragments are other biogenic components of a mold colony such as the “roots” (hyphae) and support structure of the colony.  Technically, they include phialide, hyphae, mycilia, conidiospores, fruiting bodies, etc. Some of these pieces, such as hyphae, can actually result in mold regrowth, even though they are not mold spores.  From a health point of view, research has shown that individuals can experience allergic reactions to fungal fragments as well as mold spores.   Many fungal fragments are smaller than 2 micron in size and may not be adequately captured by other types of air filters.  Research has also shown that the number of airborne fungal fragments can be 10 to hundreds of times higher than the number of mold spores in the air.  Therefore, the use of HEPA air filtration is highly recommended during microbial remediation.

Further, a mold remediation job often entails removing both mold spore and particulate matter (such as drywall dust and saw dust) generated during removal activities.   Studies have shown that these airborne particulates have two peak sizes in the atmosphere.  One peak is around 10 microns in diameter and accounts for a majority of the particulate mass generated.  The other peak is around 0.03-0.05 microns.  From an air pollution viewpoint, these fine particulates are correlated with possible health problems including asthma. When disturbing settled dust or generating dust during mold remediation, one will be disturbing particles that are much larger and much smaller than mold spores. Consequently, HEPA air filtration is the appropriate level of air filtration for these mold remediation projects.

It is important to ensure that HEPA-filtered equipment is truly living up to its name.  Recent field measurement of the effectiveness of HEPAs has shown that AFDs and HEPA vacuums may be discharging a significant amount of particulate matter out their exhaust portals. However, if the HEPA–filtered AFDs are used as NAMs (negative air machines discharging outdoors), then their effectiveness really is not a significant question. (Assuming there is no recirculation back into the building). It is only when a HEPA is used indoors as an air scrubber or in a HEPA vacuum that this issue is critical.  For more information see “Are Your HEPA Filters Doing What You Expect Them To?” Indoor Environment Connections, Vol. 8, Issue 12, October, 2007 pp. 40-43.147

In the validation of HEPA filters in clean rooms, typically, "1" or  "0" counts over the whole filter area is the acceptable validation criteria.  (30 second sampling time per point).   It would normally take 4 hours to completely validate a typical 4' x 4' HEPA filter bank! This seems unrealistic for a HEPA field certification protocol for the microbial remediation industry.

Clean room HEPAs are in a permanent HVAC system.  They are not beaten around, shaken and transported on a normal basis like remediation equipment is.  Consequently, one would not expect them to be compromised as easily as field equipment would be.  Should remediation equipment be expected to perform to the same level of filtration effectiveness as a clean room HEPA?  Should a HEPA filter "Unit" be what it is claimed to be, at least 99.97% effective at 0.3 microns?  Unfortunately, based on the limited research to date, even some brand new, out of the box "HEPA" equipment fails this effectiveness standard.

"HEPA" filter manufacturers point out that their filters are HEPA filters.  Some attempt to blame elevated particle counts on carbon particulates from the motor.  However,  manufacturers typically ONLY certify (and test) the FILTERS as being HEPA – do NOT the whole unit - with the filters installed!  This is not a good situation.  Claiming such units are HEPA filters is misleading and gives a false impression of the actual effectiveness of portable HEPA air filtration units. A review of the design and construction of some portable "HEPA" filter units showed no seal between the suction motor and the filter! This design guaranteed that some room air actually would bypass the HEPA filter and consequently the unit would not work properly.

Fortunately, some portable HEPAs do work properly.   These units have single digit counts in the exhaust air stream which should be the criteria for indoor air scrubbers and HEPA vacs.  This means that NO particle count for any size range should exceed 9 p/m3.   Two to 3 samples of the exhaust air stream is usually sufficient to evaluate if  a unit is functioning properly.  If you get a reading in the thousands after a 20 second sample, you don't need four hours of air sampling to say you have a problem..  On the other hand, trying to "Fix" a portable HEPA unit so that it passes this criteria can be complex and time-consuming.

As for "portable HEPA vacuums," we have not found one yet, new or old, that performs to HEPA criteria.  The best ones have particle counts in the 100s.   We have been leaning towards recommending HEPA vacuums be placed in front of HEPA NAMs  and then long hoses be attached - similar to central vacuum systems.  This issue is discussed further in Chapter 4, Section A.

E. Why Do PRV for Mold Remediation Projects?

The answer to this question has public health, political, social, economic and legal implications.  One important question is whether mold exposure is an actual serious general public health hazard or whether the mold hazard is more of a media-generated health hazard.  There are a number of studies that link mold and damp conditions to some respiratory symptoms and disease. However, there are many health effects reportedly attributed to mold exposure that we have not been able to prove with any degree of scientific certainty. 
1.  The Absence of Evidence

The water damage restoration industry has existed for many years. Millions of homes and businesses have been restored after floods, fires, hurricanes and tornados during the last few decades – including any accompanying mold contamination. Historically, these restoration jobs were typically performed with no final air or surface clearance testing to substantiate an effective remediation.  Yet, there are no documented studies showing health problems from these older remediation projects. Therefore, is quality assurance testing in the form of PRV really necessary?  If remediation was done successfully for so many years without PRV testing, why do it now?  On the other hand, the issue of potentially inadequate mold remediation in previous restorations has not been studied as an issue.  “The absence of evidence may not necessarily mean the evidence of absence.”

Consequently, we risk passing laws and regulations that increase the cost of mold remediation without knowing whether a real significant health benefit will be realized. Further, with a trend toward diminishing insurance coverage of mold related damage, homeowners will pay an increasing percentage of remediation costs themselves.  Therefore, an added cost due to regulatory requirements could result in some homes that need to be remediated will not be fixed due to budgetary constraints.

2.  Potential Liability

Probably the main reason for doing PRV is the question of potential legal liability. With no test data to show due diligence at the completion of the project, the contractor or consultant only have their “perception” and “experience” to use defending their work against an injury claim.  No remediation company wants to be sued and then have to respond in court to questions of why they did not test to make sure their job was done correctly.   “We test drugs to make sure they are safe, we test cars to make sure they are safe, we test air quality to make sure it is safe, so why didn’t you test the air to make sure it was safe for the plaintiff?”  Responding to that statement by saying, “There is no law that says I had to,” sounds rather cold and heartless.  Or you could reply,  “We don’t know what is safe and the United States does not have any mold exposure standards.”   The plaintiff’s lawyer would reply (and has in over a dozen cases), “There are mold exposure standards in 30 industrialized countries, and recommended guidelines by 6 trade organizations, including US trade organizations.  Did you just ignore these standards?”  Clearly, the lack of enforceable mold exposure standards in the US does not relieve a contractor or consultant of potential liability.

3.  Insurance Company Requirement

Many insurance carriers also require that PRV be conducted at the conclusion of a mold remediation job.  This often applies to the property insurance carrier who is paying for the remediation as part of a water damage claim and to the remediator’s general liability or E & O insurance carrier.  Also, when a home is being sold, PRV documentation for previous water intrusions should be disclosed to the prospective buyer.

4.  Public Relations Issues

Another reason PRV is conducted is for public relations reasons.  Sampling is often conducted to ease the worried minds of the owners, occupants, or attorneys.  This is especially true after the extensive media coverage of the “toxic mold” issue.  Few building owners or occupants understand that a significant number of samples need to be taken in order to quantify a space with a very high degree of scientific certainty.   However, even after explaining the uncertainty of limited sampling, most clients are unwilling to pay for an expensive sampling protocol due to typical economic constraints. Consequently, a consultant or remediator may be limited to a few post-remediation samples of the environment. Fortunately, statistical analysis of even a few samples can show some degree of scientific certainty, especially if the levels are very low.   (See Chapter 8 on statistics for more information.)  Regardless of these limitations, PRV is still widely used in an attempt to assure building occupants, homeowners or other interested parties that the remediation has been conducted successfully and the environment is safe to reoccupy.

5.  The Need for Consistency in PRV Protocols

To further complicate this issue, consultants who conduct PRV use whatever approach they deem appropriate based on their training and experience.  Unfortunately, this varies considerably – from white glove testing to grab air samples to surface testing every 10 square feet.  Widely differing PRV criteria by different IEPs makes it difficult for the remediator to know what is expected of him and what standard he will be judged against.  That is why a risk-based set of PRV protocols needs to be developed and agreed upon by the industry to provide the most appropriate response to each unique situation.

This is not to assume that an elaborate PRV protocol is required for all mold remediation projects.  A  visual inspection may be sufficient PRV for properly conducted, small-scale projects involving only a few square feet of mold in buildings that do not have immunocompromised occupants.  But the actual method and criteria for making the professional judgments of when testing is or isn’t necessary, needs to be defined.

Chapters 5 will begin to explore the premise that mold and bacteria remediation projects can be conducted at one of a number of levels of cleanliness assurance, depending upon the circumstances of the remediation.  Factors such as cost, insurance coverage, type of structure, use of the facility, potential health effects, population at risk, and other factors can be combined to define how much evidence is necessary to document the level of cleanliness.  Such varying degrees of cleanliness assurance are found in asbestos regulations, where one test method (TEM) is used for clearance testing is regulated in large school abatement jobs (<70 structures/mm2) and another (PCM) is recommended in other situations (< 0.01 fibers/cc.)

But we need to overview the “state of the art” as it exists for microbial PRV before we extrapolate to a logical conclusion. Chapter 2 provides an overview of numerous microbial restoration and remediation guidelines and regulations that define when PRV should be conducted and what form it should take.


         If I have seen further it is by standing on the shoulders of giants.
                        Isaac Newton, Letter to Robert Hooke, February 5, 1675.