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Should Laboratories Determine If A Mold Problem Exists?
Jason Yost • November 15, 2022
Given the complexity of interpreting laboratory results, can one really rely on the laboratory determining whether a problem exists in the sampled building?
Indoor air quality as a scientific discipline is evolving as our knowledge of the subject increases. For example, when people first began to take air samples for mold, they believed an indoor/outdoor comparison of mold spore levels was sufficient in determining if and where a problem existed. Today, the indoor air quality industry knows this isn’t true.
So, given the complexity of interpreting laboratory (lab) results, can one really rely on the laboratory determining whether a problem exists in the sampled building?
1. Laboratory results by themselves should not be used alone to form the basis of one’s data interpretation. Visual inspection of the site, site location and nearby land use, understanding the site history, identifying indoor micro-climates, and interviews with affected occupants should play a major role in one's interpretation; in fact, they should form the basis of one’s sampling strategy. Without this information, it is easy to misinterpret the laboratory’s findings. I’ll give you just one example:
Outdoor mold spores require two things, in adequately proportion and force, to infiltrate and impact the indoor environment: a pathway (how are they getting through the building envelope to gain access indoors?) and a transport mechanism (i.e., a force that adequately transports them through that pathway to the indoor environment). If one doesn’t take these things into account, they may assume that the source of indoor airborne mold spores is the outdoor environment, when they may not be, or may assume the airborne mold spores in one room is a result of mold growth in another room.
Here are a few reasons one shouldn’t:
2. Mold counts have spatial, geographic, local land use, seasonal and diurnal variability just to name a few. This variability can be orders of magnitude different in samples that are taken a few minutes apart! An interpretation of one’s samples that is based on subjective, invalidated internal criteria developed by a laboratory is a great way to make incorrect conclusions. Here’s one example:
When it first starts to rain, one may find that uncommon mold spore types are found in the outdoor sample because the raindrops are aerosolizing spores from the leaves and branches on the ground upon impact, but, minutes later, as the rain persists, one may find the outdoor air holds little to no mold spores because the rain has captured and suppressed the mold spores onto wet surfaces.
3. We know that different sampling devices result in different collection efficiencies that depend on the spore size. This variation is significant when comparing sampling devices. These collection efficiency differences are not considered by labs offering this type of data interpretation.
4. The process by which the sample was collected can positively or negatively impact the laboratory's analysis of the sample. You see, whenever a mold assessor seeks to interpret the laboratory's results, they will look at the column listed spores/m3. There are many reasons for this, but the most important is that when interpreting laboratory results, one should do so in a way that is standardized. The raw count column is not standardized; therefore, it is best to utilize the spores/m3 column. Here's where a problem arises for the laboratory. The laboratory will extrapolate - from the raw count (i.e., the actual amount of spores counted by the laboratory technician) - the spores/m3 via a mathematical formula that doesn't take into account how the sample was collected - only the amount of air that passed the sampling media. It assumes that the only spores captured by the sampling media were those directly drawn in by the sampling pump; however, something as simple as how the sampling media faces (e.g., up or down) could impact that variable. When facing up, the sampling media will collect those spores drawn into it as well as those settling from the air (like dust settling on our furniture); when facing down and the surfaces below the sampling media aren't disturbed, it will only collect those spores drawn in by the sampling pump. The laboratory doesn't know how the samples were collected and may report findings that cannot be relied upon by themselves to determine if a problem exists in your home or office.
With all of this in mind, you may be asking: What are you really getting with mold sampling and laboratory analysis? The sole purpose of a laboratory is to provide the mold assessor with independent, objective, and scientifically defensible data to be interpreted through the lens of a professional, site-specific mold assessment. When performed and utilized properly by the mold assessor, they provide the mold assessor with additional information for technically accurate determinations and reporting of your building's condition relative to mold.
However, when the mold assessor relies on laboratories that offer him or her “statistical data interpretation”, a "score", or tell him or her whether their samples have elevated mold levels, they aren't providing you an honest, scientific analysis of your home or office. Rather, these mold assessors are jeopardizing their reputation and exposing themselves to professional liability. Such service fails to deliver technically accurate mold assessment determinations (e.g., is the indoor air quality compromised due to elevated mold spores or not?). No one can afford that kind of service, nor should they receive such service.
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