Biocide Use and IICRC Standards
A: Before addressing your question in detail, let's look at what the two standards actually say with regard to biocide use.
According to the S500 Section 1.2 (Purpose), "It is the purpose of this standard to define criteria and methods to be used for assessing water damage and establishing restoration procedures."
The S500 specifically recommends that biocides be used as a backup, not primary, method of controlling microbial growth on "clean" Category 1 water losses. Section 11.2.10 states, "To the extent possible, microbial growth must be controlled by removing water and reducing humidity. If drying is not accomplished promptly, microorganisms are likely to grow."
However, the S500 also recognizes that, on the same type of loss, biocides may be helpful when the primary method of limiting microbial growth by controlling moisture is not possible or practical. The same section continues, "When there has been a delayed response or an inability to eliminate moisture, the application of a biocide, following initial water removal, may help prevent some microbial growth."
Therefore, for this particular application, the S500 is not prescribing biocides to solve existing microbial problems. It is merely stating that biocide use may be appropriate as a backup to help prevent such problems from developing when moisture control or mitigation services cannot be implemented quickly enough.
Section 12.3.8 (Initial Decontamination) states, "...decontaminate sewage-damaged materials by spraying with, or immersing within, a biocide solution...The objective of initial decontamination is to commence the reduction...of microorganisms as quickly as possible."
Section 12.3.14 (Secondary Biocide Application), "After thoroughly cleaning all contaminated materials, a second application of biocide must take place...These chemicals are capable of killing or inactivating pathogenic microorganisms...Evaluate factors that affect the success of disinfection. These include, but are not necessarily limited to: organic matter present, extent of prior cleaning, type and level of microbial contamination, type of biocide required, concentration and time of exposure to the biocide required, and the nature of the material to be decontaminated."
The general context of Section 12 and of the remainder of the S500, including the first three chapters of the Reference Guide (covering microbiology associated with water damage, its health effects and the use of biocides) make it clear that use of biocides on water-damage projects is recommended as appropriate, when properly used, for two primary purposes:
According to the preface, "This document is written for use by those involved in the mold remediation industry, primarily for mold remediation companies and workers, and secondarily, for others who investigate mold complaints, write remediation specifications, protocols and/or procedures and manage remediation projects." It specifically notes that the S520 and the S500 address different issues: "While the S500 was a significant step forward in the water damage restoration industry and recognized the problem of microbial growth from water damage, it was not intended to provide specific guidance on the subject of mold remediation."
Despite what you may have heard, the S520 does not prohibit the use of biocides on mold-remediation projects. Rather, it discusses the limitations of what the application of such products can accomplish. Because of these limitations, it was decided that biocides have limited efficacy in mold remediation and that physical removal of mold spores and fragments is a much more effective approach. As Section 4.4 (Principles: Contaminant Removal) of the Standard states, "It is highly recommended that mold contamination be physically removed from the structure, systems and contents to return them to Condition 1 (normal) status. Attempts to kill or encapsulate mold generally are not adequate to solve the contamination problem."
The principles of biocide use endorsed by the S520 (Chapter 10 of the Reference Guide, page 119) are drawn directly from "ACGIH Bioaerosols: Assessment and Control."
"15.2 Remediators must carefully consider the necessity or advisability of applying biocides ... The goal of remediation programs should be removal of all microbial growth. This generally can be accomplished by physical removal of materials supporting active growth and thorough cleaning of non-porous materials. Therefore, application of a biocide would serve no purpose that could not be accomplished with a detergent or cleaning agent."
"16.2 Biocide use should not be considered if careful and controlled removal of contaminated materials is sufficient to address a problem."
"16.2.4 Biocide application is not recommended in the restoration of water-damaged indoor environments except where they have suffered extensive sewage backup. Widespread pollution from raw sewage represents a significant health risk from a variety of infectious agents, and biocides may help to control and contain these agents during the restoration process..."
Applying these principles, the S520 discourages the use of biocides. Chapter 7 of the Reference Guide, page 82, states, "Biocide application is discouraged and is not considered effective for mold remediation."
However, the S520 also recognizes that, "there may be specific instances where professional judgment dictates that biocides be applied." Thus, it discusses in detail, in Chapter 7, the situations where deviation from removal processes might be appropriate, stating, "The Principles of Mold Remediation (Sections 4.3 and 4.4 of this Standard) state that mold must be controlled at its source. Further, it is highly recommended that mold be physically removed during remediation, and that attempts to kill or encapsulate it are inadequate remediation measures. At the same time, these principles recognize that unique circumstances may arise and that biocides and encapsulants may be considered in specific situations."
Nowhere in the S520 does it state that biocide use is never appropriate. Rather, in agreement with "ACGIH Bioaerosols: Assessment and Control," it recognizes the fact that biocides are not effective at solving mold contamination problems; that requires physical removal of contaminants. It leaves the door open for biocide use in unusual situations, on a case-by-case basis. Those who wish to use these products and still be in compliance with the S520 need only demonstrate why biocide use is appropriate on the particular project.
S500 vs. S520
The two documents do not always appear to be in complete agreement on the subject of biocides. There are a number of reasons for this:
The S520 was written five years after the S500. In the meantime, things have changed. The S520 had to specifically address issues that were really not much of a problem when the S500 was being written. The degree of agreement is actually quite remarkable when you take into account the enormous changes in the water damage and mold remediation industries during the past five-year period.
The two documents cover very different issues. The S500 addresses mold contaminants only in passing, and even then its primary emphasis is, appropriately, on the prevention of mold growth, not its remediation. The S520, in contrast, addresses the very different problems of how to deal appropriately with mold contamination that has already developed.
The primary purpose for which the S500 recommends biocide application is when dealing with a significantly or grossly contaminated water damage situation (Category 2 or 3). In this situation, the biocide is intended to kill or inactivate pathogenic organisms, mostly bacteria, viruses and parasites. As noted above, this application is directly endorsed by the S520 and "ACGIH Bioaerosols: Assessment and Control."
The S520 also notes that biocide application may be appropriate as a preventative of microbial growth on "clean" water (Category 1) projects. The primary purpose of such an application is to control bacterial growth when drying is delayed, with some possible effects in limiting mold germination and growth. Since the purpose is not to deal with existing mold contamination but rather to prevent it, such use in no way contradicts the S520.
To answer your original question, at first glance there appears to be significant differences in the recommendations of the two documents with regard to biocide use. However, most of the apparent contradictions disappear with careful examination of what the documents actually say. Those that remain are easily explained by the fact that the S500 and the S520 are talking about different subjects, and by the five-year gap in the date of production. The S500 is presently under revision. It is logical to expect that the revision committee will address any purported contradiction between the two documents, including the use of biocides. The IICRC has a public review process. If you have comments about any of the standards you can go to http://www.iicrc.org/standards-review.html and comment online. Any comments submitted will be forwarded to the appropriate committee for review.
So, which document should you follow? Simple. When doing mold remediation, follow the S520. When doing water damage restoration, follow the S500. However, a complicated situation arises when you must dry a contaminated building. Obviously, you must get the building dry - following the S500 - but you must do so in such a way that you do not cause or allow the spread of microbial contaminants. Where you have a contaminated building that needs to be dried, you must figure out how to combine the containment provisions of the S520 with the recommendations for efficient drying in the S500. Some water-damage restoration training classes are already addressing these issues.