Turning Up the Heat
April 10, 2006
A: First of all, I personally believe that heat is an effective method of solving bacterial problems in buildings. However, it is important to clarify what we mean by remediation. Both mold and sewage damage cleanup fall into this category. Let's begin with hot air drying in general and then discuss sewage (bacteria) and mold.
Currently there are several franchise and licensing companies that offer hot air for drying and pest control. There are also indirect fired heat exchangers that can be used for this purpose. Outdoor air is processed through the equipment where it is heated. The hot air is forced into the indoor environment or crawlspace to promote evaporation and then exhausted back to the outdoor environment. It is a process of ventilation, not dehumidification.
The indirect fired heat exchanger systems provide clean heat for drying and do not introduce combustion gases and water into the environment. The internal temperature of the heated indoor environment can range from 120 degrees to 160 degrees. Of course, in any instance where heat is used within a structure, fire safety and prevention must be considered. Also, temperatures above 160 degrees (and sometimes lower) may cause damage to certain building components or contents, so monitoring and an understanding of how building components react to heat is essential. The units are generally placed outside the building, with duct work attached to the clean air exhaust. Locating equipment outside the building may result in safety and security issues. There are other units on the market that are custom built for this purpose that have design variations.
An advantage of using heat for sewage remediation in crawlspaces is the ability for heat to assist in drying the crawlspace. The elevated temperature of the air makes it "thirsty," so it has the ability to hold more moisture. This is only an advantage if the moisture-laden air is exhausted to the outside. If the air isn't exhausted, but is allowed to re-circulate, the moisture may condense on cooler surfaces causing additional damage.
For years we have utilized a chart in our training classes that is derived from a study that was performed by the World Bank in 1980. It shows, among other things, that sewage-related organisms will naturally bio-deteriorate in six to 12 months if left in the soil. It also indicated that by heating the environment that sewage-related organisms (bacteria included) would die in a matter of hours.
Other options for remediating sewage in soil include soil removal and replacement; or covering the soil with a mat or polyethylene (in some cases in conjunction with depressurization using a gas mat system connected to an exhaust fan). Other options, such as using biocides or lye/lime, create other problems and have not been found to be practical or effective solutions. But soil removal is labor intensive, and bio-remediation takes considerable time to be effective. Heat, on the other hand, can speed up the process and reduce costs.
There are several issues to consider when using heat in a crawlspace. You need to ensure that the pressure differential between the crawlspace and the living area remains negative relative to the crawlspace. Studies have shown that air infiltration from crawlspaces into a structure is common. If you force air into the crawlspace, it will add pressure and increase the infiltration. That is why maintaining negative pressure in the crawlspace while drying or remediating using heat is important.
Another consideration is the depth to which the sewage has penetrated the soil. The deeper the penetration, the longer the heat is needed to raise the temperature of the soil. What is likely to occur, in most situations, is the pathogens in the top layer of soil are killed, but may remain active in cooler depths of the soil. It is also important to remember that even though elevated temperatures kill pathogens, the organic material remains and may still result in major odor problems over time.
The use of heat has been proposed to assist in the process of mold remediation. At this time, the research does not fully support the use of heat as a complete remediation option. Our company has conducted some preliminary research into the possible effectiveness of heat on actual mold growth. This was a preliminary study, designed to explore the ability of heat to kill mold spores and hyphae after water damage in buildings.
The study was conducted by collecting dry and wet culture swabs from previously identified mold growth of Penicillium and Aspergillus. The swabs were placed in clean sealed containers that would contain the organisms, but allow the heat to penetrate. Identical controls samples were also prepared. The controls were maintained at room temperature. The dry and wet mold samples were placed in a heated shed type building that was kept at a temperature around 160 degrees. Half of the treated samples were exposed for a period of approximately one hour. The other samples were exposed to the heat for eight hours. The results demonstrated no apparent reduction in the levels of fungal growth between the controls and the "dry" spores that were cultured after exposure to heat for either of the two treatment periods.
The "wet" spore control culture demonstrated growth consistent with that found in the "dry" spore cultures. The "wet" spore heated culture demonstrated no growth for either of the exposure times. The significance of this result is not clear since the cultures were not processed promptly after collection due to communication and shipping problems. The control samples were handled identically with the treated samples with the exception that the controls were never exposed to temperatures over room temperature.
An explanation for the absence of growth from the short term and long term exposure to heat for wet samples would also require additional investigation. These same kinds of results were also observed when similar mold cultures were exposed to heat in an oven operating at approximately 170 degrees for 24 hours - there was not a significant reduction in the viability of the dry spores.
Even if heat were able to kill mold spores, it probably would still not be an acceptable technique for treating mold in crawlspace since the "dead organisms" are still problematic. The EPA in its publication "Mold Remediation in Schools and Commercial Buildings" states: "The purpose of mold remediation is to remove the mold to prevent human exposure and damage to building materials and furnishings. It is necessary to clean up mold contamination, not just to kill the mold. Dead mold is still allergenic and some dead molds are potentially toxic."
According to a recent position paper published by the "Journal of Allergy and Clinical Immunology" (Volume 117, number 2, pgs 326-333): "Allergic responses to inhaled mold antigens are a recognized factor in lower airway disease (i.e., asthma)." The position paper also states hypersensitivity pneumonitis "is an uncommon but important disease that can occur as a result of mold exposure." Both of these conditions can result from dead spores.
At present, the mechanism that causes toxicosis and the concern over inhaled mycotoxins produced by molds remains unclear. However, it has been shown that certain mycotoxins, such as satratoxin produced by Stachybotrys, can penetrate the skin and cause an adverse reaction. Ingestion has resulted in serious toxicity in the food industry.
For this reason the food industry has significantly researched techniques to destroy mycotoxins or rendering them harmless. In "Food Safety: Foodborne Illness" it is stated that "these substances [mycotoxins] are not protein and are not destroyed by heat. The best methods of control for mycotoxins are to prevent contamination and to prevent the growth of mold." The International Crops Research Institute has stated that mycotoxins known as "Aflatoxins in dry state are very stable to heat up to the melting point." The melting point for Aflatoxins range from 237 degrees to 299 degrees. Finally, according to the Queensland Government Department of Primaries Industries and Fisheries, "Heating is not a satisfactory method for detoxifying fungal mycotoxins..."
Heat appears to be a useful tool for some applications and not others. As with any tool, it is important to learn what it can and cannot accomplish. This is obviously important to protect your company against liability and to be sure the services you offer are effective.