Looking Beyond the Barrier
Water Intrusion and the Research Environment
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In the aftermath of a major water intrusion event, the appearance of plastic containment and specialized equipment implies that the restoration work reflects practices anchored in science. But to understand what happens during the restoration process, it is important to look beyond the plastic barrier. Awareness of the art and science behind water restoration strategies and fundamental psychrometry—the science of drying—allows industrial hygienists to make informed decisions that prioritize occupant safety and achieve successful restoration of the building with minimal damage to the structure or contents. Work performance contrary to industry best practices can lead to costly mistakes or unintended harm to occupants. This article strives to shed light on the lesser-known aspects of the water restoration process. FROM WET WALLBOARDS TO MOISTURE MAPS When assessing water intrusion events, particularly in cases of severe flooding, the first step is to conduct a comprehensive assessment of the affected area. This includes a thorough site-specific safety survey to identify suspected contaminants present in the source water and quantify the extent of wet surface areas. It’s critical to assess building products for legacy hazards such as asbestos, silica, and lead-based paint. Once safety risks have been addressed, the next steps involve establishing “dry standards” and drying goals. Dry standards refer to site-specific approximations of the moisture level of the building material prior to the water intrusion event. Moisture mapping utilizing specific detection equipment is a critical aspect of the restoration process, ensuring that affected materials are restored according to drying goals. To document and indicate changes in the moisture content of impacted materials over time, industrial hygienists maintain a moisture map and restoration monitoring logs. In the professional water damage restoration industry, it is standard practice to document the drying progress by using a daily drying log. The ideal moisture content for these materials is used as a benchmark to assess whether the drying goals have been met. Factors that help determine the success of restorative drying may include the following: • category of water (sanitary, gray water, or black water) • classification of the estimated evaporation load • porosity and permeability of the affected materials • project complexities and limitations • building assembly requirements In situations involving gypsum wallboard, also known as drywall, the response algorithm may require the physical removal and proper disposal of wet materials. The choice between drying the drywall in place or opting for removal hinges on the category of water and likelihood for timely drying. Removal or in-place drying may also be dictated by what is behind the drywall, such as insulation. Generally, drywall contaminated with sewage or other harmful agents can’t be disinfected and restored to a pre-loss condition, and therefore must be removed from the structure. Even seemingly clean water that has filtered through the building may have absorbed contaminants and should be treated as potentially contaminated. Conversely, when drywall has been affected by clean, sanitary water (Category 1), it may be a candidate for drying in place. Understanding the phenomenon of water wicking provides valuable insights into the complexities of moisture movement through drywall. This knowledge aids in understanding the risk of mold growth and the probability of successfully restoring drywall. Depending on when the drywall is examined after a water intrusion event, the visible water line, if present, may differ from the actual leading edge of moisture. An EPA study found under test conditions that the visible water line on a section of drywall reached approximately three inches after two days of continuous immersion in half an inch of water. However, the leading edge of actual moisture measured by a pin-type moisture meter reached nearly thirteen inches. The study demonstrated that moisture wicks up into drywall at nonlinear rates, slowing dramatically after the first day. Simply observing the visible moisture line does not tell the whole story. This wicking phenomenon can be greatly influenced by how the drywall was installed. For example, drywall attached to wood framing is typically suspended approximately one-half inch off the floor, which will significantly reduce or eliminate wicking compared to drywall that is flush with the floor. Wicking is also likely to occur at a greater rate if the drywall is attached to metal framing. Furthermore, the hygroscopic characteristics of the gypsum material, the paper type enveloping the gypsum, and the presence of finishing treatments such as paint influence drywall’s absorption capacity. When dealing with a water intrusion event, it is critical to understand how far the moisture has travelled before determining appropriate mitigation strategies. Relying solely on visual inspection is insufficient; instead, a scientific method should be employed to accurately assess the extent of water damage and log it in the drying record.
The visible water line, if present, may differ from the actual leading edge of moisture.
THE FLOOD-CUT FALLACY The information logged in the drying record will inform the preferred mitigation strategy, including the use of “flood cuts,” which remove a portion of the affected building materials, typically drywall, above the waterline. Flood cuts are particularly important when drywall has been exposed to water containing hazardous substances or to prevent mold contamination. In cases where there is substantial water damage or a delay in the drying of drywall, a flood cut may be necessary.
Flood cuts are typically made relative to the damaged area, six to twelve inches above the wet drywall. But as EPA’s water wicking study shows, the visible water line does not necessarily reflect the extent of moisture migration; it’s more appropriate to cut above the moisture gradient rather than the water line. In other cases, “absolute” flood cuts are recommended at some predetermined level, assumed to include the extent of the affected area. Since drywall is manufactured in 48- by 96-inch sheets, the absolute flood cut method suggests cutting horizontally 24 or 48 inches above the floor to maximize efficiency and reduce waste.
In the absence of a drying record or if the water intrusion event overwhelms the resources of the restoration team, an absolute flood cut may be the logical decision. However, it’s imperative to approach this convenient and time-saving approach with caution, as it could inadvertently lead to the development of hidden mold due to missed moisture. Mechanical devices are often used to cut drywall fixed on walls, which produces fine particulates including gypsum and silica dusts. Building finishes often include flame retardants, plasticizers, and chemical preservatives that may be aerosolized by mechanical cutting. Utilizing shrouded cutting tools and vacuuming at the point of operation is common to manage dust contamination, but studies have reported that vacuums can increase the airborne concentration of particles up to 61 times compared to background levels. Increased particulate matter introduces exposure risk to building occupants and contaminates sensitive environments such as healthcare facilities and research laboratories. Whereas a shop vacuum may be familiar to the construction industry, a HEPA (high-efficiency particulate air filtering) vacuum held at the cut point is the appropriate method for controlling dust emissions.
EXCEPTIONS TO THE 48-HOUR RULE In certain instances, following a water intrusion event, restoring drywall in place may be more practical than removing it. EPA suggests that if there is no obvious swelling and the seams remain intact, drying in place can be a suitable strategy, especially when the water involved is clean and drying occurs within 24 to 48 hours. This period is often regarded as critical for preventing mold growth, according to nationally referenced guidelines. However, the reliability of the 24 to 48-hour timeframe is still a subject of inquiry among industrial hygienists.
For example, a study assessing mold remediation practices did not detect mold growth on drywall after a one-week incubation period, which challenges the notion of the 24 to 48-hour recovery window. Conversely, another study investigating mold growth on drywall found that under favorable conditions, mold can grow microscopically within a few hours and visibly within several days.
The uncertainty of mold growth occurring 24–48 hours after building materials are exposed to water raises questions. New York City’s “Guidelines on Assessment and Remediation of Fungi,” published in 2002, gained prominence for recommending the drying of water-damaged materials within 24 to 48 hours of the incident to prevent mold growth. Interestingly, the 2008 revision of the guidelines didn’t mention a timeframe. Another commonly referenced timeframe can be found in CDC’s “Guidelines for Environmental Infection Control in Health-Care Facilities,” which recommend removal of building materials if they are not dried within 72 hours.
It’s important to emphasize that the timeframe for mold colonization varies depending on environmental conditions. Various factors, such as temperature and surface moisture, contribute to mold growth and influence the window of risk. Therefore, the reliability of the 24 to 48-hour guideline can be called into question when mold is not visibly present within this period, despite contrary expectations.
While the 24 to 48-hour guideline serves as a practical reminder that immediate action is necessary, it’s important to consider the specific circumstances, environmental conditions, and expert assessments from water restoration professionals when deciding whether to restore building materials.
HOW “STANDARD” ARE STANDARDS? Mold growth poses concerns for the health and safety of building occupants and can lead to legal liabilities within the workplace. While there is no OSHA-promulgated standard specific to bioaerosols originating from damp building environments, the prevention of mold growth is a fundamental strategy for managing risk and safeguarding the well-being of occupants.
ANSI/IICRC S500, Standard for Professional Water Damage Restoration, is the recognized guideline when performing water damage restoration. This consensus standard places the responsibility for identifying and correcting the underlying source or cause of water intrusion leading to the water damage on the property owner rather than the restorer, even if the owner contracts with the restorer to perform the restoration activities. For this reason, it’s prudent to hire a reputable water restoration company with expectations established within the service agreement.
The standard introduces key principles of water damage restoration, building and material science, worker safety and health, psychrometry, and drying technology. It also outlines the qualifications of restorers, which include their education, training, and experience, to safely and effectively carry out restoration work. ANSI/IICRC S500 recognizes the art and science of water restoration activities. The standard defines “indoor environmental professionals,” or IEPs, as individuals with skills and experience in sampling methodologies and assessments, remediation protocols, and post-remediation verification clearance services. Both the restoration contractor and the IEP may be involved in categorizing the water to determine whether remediation or demolition is required and the evaporation load necessary for successful restorative drying. Understanding and employing psychrometry to estimate the minimum dehumidification capacity in a water-damaged environment is a significant competency for restoration professionals.
The standard also addresses challenges such as limitations, complexities, or complications that may result in disagreements between parties. All professionals involved in a water damage project should evaluate and address any known or suspected hazards at the workplace. IEPs may be involved to provide more comprehensive sampling of a building if occupants are concerned about the indoor air quality or have specific exposure concerns due to the water intrusion. Failure to address these hazards or exposures could introduce liability and further need for corrective actions.
MULTI-EMPLOYER RESPONSIBILITIES Water damage restoration projects often require employees from different employers to work together. In the context of a laboratory responding to a water intrusion event, OSHA’s multi-employer citation policy helps delineate responsibilities among the different parties. Using the laboratory environment for illustration, the lab owner is the controlling party and bears responsibility for informing the water restoration company about the presence of chemical, physical, and biological hazards within the laboratory. The restoration company is responsible for safeguarding its employees. This includes the duty to proactively inquire about site-specific hazards and understand control strategies implemented within the host employer’s workplace.
A robust health and safety management program ensures affected employees receive training on hazards specific to the work environment. For example, the host employer may need to train its employees on hazards related to the water intrusion event such as electrical hazards, slip and fall hazards, biological and chemical hazards in the water, silica dusts, and so on, whereas the contractor should train its employees on hazards unique to the project site such as laboratory chemicals. Bulletins published through OSHA’s Temporary Worker Initiative remind us that both employers are responsible for ensuring employees know how to do their work safely, can identify hazards, and understand control and protective measures.
INSTRUMENTATION One way to assess the extent of damage following water intrusion is by determining the extent of water infiltration or migration into building materials. Several instruments are employed for the water assessment, including infrared cameras, moisture meters, and thermo-hygrometers.
Infrared Cameras Infrared (IR) cameras, also known as thermal imaging cameras, detect differences in heat signatures. While they cannot directly detect moisture, they are able to rapidly detect differences in the heat signature caused by the presence of water without damaging the wall in the process. The basis for detection of water using thermal imaging is primarily that evaporative cooling will cause moist material to have a lower temperature than the same material when dry. However, under certain environmental conditions, especially high humidity and low temperature, thermal imaging is unable to optimally detect moisture due to low evaporation rates and may result in false negatives.
Moisture Meters Most contemporary moisture meters utilize either pin-type or pin-less technology. Pin-type moisture meters gauge the electrical resistance between a pair of electrodes (pins) on the meter. These pins are inserted into the building material at the point where moisture levels are being assessed, providing the user a measurement of the moisture in the material between the pins, usually expressed as percent moisture content (MC%). The basis for this measurement is that the presence of water decreases the electrical resistance within a material, thereby allowing an increased flow of electricity between the pins. One drawback to using a pin-type moisture meter is that multiple readings are required to assess water content across a sizable surface area, resulting in numerous puncture holes in the process. Furthermore, the measurement depends on the length of the pins and depth they are inserted into the material, a potential limitation when dealing with thick materials such as layered drywall.
In contrast, pin-less moisture meters are nondestructive. They work by measuring the capacitance, or the amount of energy that can be stored in a material, over a large area and are ideal for comparative readings when assessing moisture in drywall. The basis for this measurement is that increased moisture in the material increases the capacitance. As with pin-type meters, the moisture detected depends on the depth of the moisture present, but pin-less meters require a flat surface for proper function, and certain units must be held in a specific orientation and pressed with light pressure for a proper reading. Caution is required with these devices to avoid inaccurate readings due to user error.
A significant pitfall of both pin-type and pin-less moisture meters is that the presence of salt or conductive material such as metal studs within the sampled area can cause false positive readings. Additionally, moisture meters are often calibrated to specific materials and target specific wood species, which requires careful consideration when interpreting measurements. Many moisture meters have settings to resolve the differences between wood types and other building materials; indeed, the Gypsum Association cautions against using moisture-meters for evaluating drywall. When used to assess wet areas, the meters should first be calibrated according to ASTM C1789, Standard Test Method for Calibration of Hand-Held Moisture Meters on Gypsum Panels. As is true for industrial hygiene instrumentation, users are responsible for understanding the application and limitations of moisture meters.
Measuring Ambient Conditions Thermo-hygrometers measure airborne parameters such as relative humidity, temperature, vapor pressure, dew point, and humidity ratio. These psychrometric readings can be used to identify rooms or areas in the building that have higher humidity prior to testing surfaces for moisture; they can also monitor dehumidification efforts related to the post-remediation drying plan.
Electrical thermo-hygrometers often function by measuring the capacitance or the resistance of a semiconductor, which changes depending on moisture levels in the air at the time the measurement is taken. These devices are both useful tools to detect overall differences in humidity between different spaces; however, they are less useful for determining the specific areas within the room that have water damage.
UNDERSTANDING RESTORATION Because industrial hygienists represent the building’s occupants, it’s our responsibility to look beyond visual cues to ensure appropriate strategies are practiced during water restoration efforts. An awareness of the art and science of restoration is important to recognize when best practices are followed in performance of the work. Understanding the nuances of water damage restoration is key to achieving effective and safe outcomes in complex environments such as laboratories and healthcare settings.
DEREK A. NEWCOMER, DrPH, CIH, CSP, is a commissioned officer in the U.S. Public Health Service and is the deputy director of the Division of Occupational Health and Safety at the Office of Research Services, National Institutes of Health, in Bethesda, Maryland.
RACHEL JOHNSTON, PhD, is a biosafety manager at the University of Georgia and is an alum of the National Biosafety and Biocontainment Training Program.
SIVARCHANA MAREEDU-BOADA, MS, PhD, is an alum of the National Biosafety and Biocontainment Training Program.
NICKY ROSE, MS, MPH, is the associate director of environmental health and safety at ThermoFisher Scientific/PPD in Richmond, Virginia, and is an alum of the National Biosafety and Biocontainment Training Program.
NATHAN SEWARD, PE, CIH, of Premier Environmental Consulting has provided environmental engineering and consulting services for overseas air force bases, high security government projects, and commercial/industrial projects.
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Building and Environment: “Impact of Vacuum Cleaning on Indoor Air Quality” (August 2020).
CDC: “Guidelines for Environmental Infection Control in Health-Care Facilities” (PDF, 2003).
EPA: “Moisture Movement (Wicking) within Gypsum Wallboard” (June 2005).
Gypsum Association: “Moisture in Gypsum Panel Products.”
Institute of Inspection Cleaning and Restoration Certification: ANSI/IICRC S500, Standard for Professional Water Damage Restoration (2021).
Journal of Occupational and Environmental Hygiene: “Controlled Study of Mold Growth and Cleaning Procedure on Treated and Untreated Wet Gypsum Wallboard in an Indoor Environment” (August 2006).
Microbiome: “Moisture Parameters and Fungal Communities Associated with Gypsum Drywall in Buildings” (December 2015).
New York City Department of Health and Mental Hygiene: “Guidelines on Assessment and Remediation of Fungi in Indoor Environments” (PDF, November 2008).
OSHA: “Multi-Employer Citation Policy” (December 1999).