Building Envelope

The Past, Present and Future of Vapor Intrusion Barriers

October 19, 2020 - by Tom Szocinski
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The Past, Present and Future of Vapor Intrusion Barriers

Vapor intrusion entered the national consciousness in the late 1970s as people sought answers to explain cancer clusters and other negative health effects arising from poor indoor air quality.

Cases like Love Canal, where 21,000 tons of toxic industrial waste had been buried underground in the 1940s and '50s, further advanced public interest in the topic. That case resulted in significant health issues amongst residents, brought significant regulatory attention to the growing problem of dangerous contaminants entering occupied spaces.

In the 2000s, engineers and scientists worked to gain a better understanding of exposure limits of volatile organic compounds (VOCs) in order to better delineate exposure pathways. The documented adverse health effects of inhaling contaminated indoor air resulting from VI showed that, depending on the chemical, exposure could lead to asthma, neurological effects, kidney damage or an increased risk for cancer.

Today, almost every hazardous waste site requires evaluation of vapor intrusion pathways, with estimates showing that one quarter of all hazardous waste sites in the United States have conditions that could result in exposure – the most common chemicals of concern being chlorinated solvents and petroleum hydrocarbons.

As demand for commercial and residential developments continues to rise, so too has public demand for safety and corporate accountability. As a result, property developers are constantly on the hunt for the most effective vapor intrusion mitigation technology in order to reduce risk and limit future liability as well as avoid millions of dollars in potential legal exposure.

The Challenges of Vapor Intrusion Mitigation

In order to properly understand how to mitigate vapor intrusion, it is important to understand its challenges.

Vapors can enter occupied spaces through a variety of exposure pathways, such as cracks in the floor slab, utility conduits or directly through concrete pores. Once inside, even low concentrations can cause several adverse short- or long-term health effects. The goal of any vapor intrusion mitigation solution is to cut off these pathways through either active or passive means.

Physical barriers are commonly used to prevent vapors from entering an occupied space. To be effective, a barrier must offer high chemical resistance, good constructability (which relates to the ease and cost of installation), and the physical toughness required to withstand stress both during and after construction.

Vapor intrusion barriers tend to have two components: 1) a base layer that provides the bulk of the protection, and 2) a sealant to prevent vapors from entering through seams and penetrations. Early barriers were adopted and retrofitted for use from the waterproofing industry. These were thin plastic sheets that had low puncture and tear resistance, but were not exceptionally chemically resistant and were difficult to seal at perimeter walls and utility penetrations.

Improvement through Innovation

While some commercially available solutions face issues such as high levels of moisture retention or leakage, market leaders continue to commit to extensive scientific R&D to upgrade each of the components of a vapor barrier to address the challenges of vapor intrusion in innovative new ways.

Chemical Resistance
The most important aspect of any VI barrier system is chemical resistance. A vapor intrusion barrier with low chemical resistance will simply allow chemicals of concern into occupied spaces.

Starting with the base layer, the industry’s latest scientific advancements started with the evaluation of different construction materials to increase the level of protection. The thin-mil plastic sheeting that had initially been adopted from the waterproofing industry had inadequate chemical resistance, while some of the high-density polyethylene (HDPE) sheeting used in subsequent barriers offered better chemical resistance – but at the price of constructability.

Knowing that aluminum is highly effective at preventing the permeation of VOCs, a base layer was created with aluminum sheeting sandwiched between flexible HDPE, providing multiple layers of protection.

Turning to the sealant, scientists sought a replacement for the styrene-butadiene rubber (SBR) core, a legacy of its waterproofing origins. While SBR was very effective at repelling water, it had the unfortunate tendency to sorb the very contaminants they were meant to protect against. Barrier experts decided on nitrile (a key component of the protective gloves used in professions that often come into contact with solvents and hydrocarbons) as an effective replacement. Around penetrations and seams, the sealant becomes the primary line of defense against vapor intrusion, with studies showing that an asphalt latex sealant with an advanced nitrile core offers ten times the protection of spray-applied, non-nitrile asphalt latex equivalents.

Incorporating both these upgraded components into a single product provides barriers a higher chemical resistance than any other product on the market, demonstrating best-in-class protection that eliminates both adverse health effects and financial liability.

The easier and faster a vapor barrier can be installed equates to more money being saved and fewer mistakes made.

The most common challenge with previous systems, such as tape-based or inflexible HDPE barriers, is properly sealing all the penetrations and seams. Even with a qualified installer, installation requires a significant amount of time to ensure a secure system protected from leaks in the most vulnerable areas.

Designed to be easily installed, today’s latest barriers are applied by rolling out composite sheets and then sealing seams and penetrations with spray-applied asphalt. With this simple method, installation is 40 percent faster compared to alternate plastic sheeting or HDPE systems. The spray-applied asphalt also makes it easier to seal around difficult positions, especially when terminating onto concrete or ABS and PVC piping, saving even more time while still creating a robust system.

The new nitrile-advanced asphalt latex is also engineered to offer fast curing times that can occur at relatively low temperatures, helping to save time and money while expanding the range of conditions under which it can be installed.

Physical Toughness
When the physical integrity of a barrier is compromised, its ability to keep vapors out is significantly reduced. Previous vapor barriers were easily punctured or torn, rendering them incapable of handling the stress of a construction site or basic post-installation usage.

By improving the base layer, industry leaders have improved the physical robustness of the overall system. Composed of a metallized film laminated to a geotextile, a co-polymer polyethylene and a tear resistant PET (polyethylene terephthalate) with reinforced grid structure, the vapor barrier provides superior durability. These fortified components are designed to withstand the stresses of a typical construction site.

Unlike other available vapor barrier systems, they are less likely to incur damage during construction, limiting the need for time-consuming repair work and additional costs in maintaining the overall integrity of the system.

A lasting system should be backed by an industry-leading warranty and network of certified applicators trained in quality-control measures designed to ensure peace of mind for developers and occupants alike.

The Future of Vapor Intrusion Mitigation

From thin plastic sheets that were a remnant of a waterproofing past to the latest barriers that utilize advanced metallized films and nitrile-cores, vapor barriers have evolved significantly since the recognition of vapor intrusion as a significant environmental issue. Constantly looking towards the horizon, leaders in the space continue to research new materials and develop novel tools and techniques to create cost-effective solutions for architects and engineers seeking to both provide safe indoor environments for building occupants and help developers reduce their legal exposure. Taking lessons from the past will ensure a safer future.

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