Concerning the implications of carpet on indoor chemistry and microbiology
Carpet and rugs currently represent about half of the United States flooring market and offer many benefits as a flooring type. How carpets influence our exposure to both microorganisms and chemicals in indoor environments has important health implications but is not well understood. The goal of this manuscript is to consolidate what is known about how carpet impacts indoor chemistry and microbiology, as well as to identify the important research gaps that remain. After describing the current use of carpet indoors, questions focus on five specific areas: 1) indoor chemistry, 2) indoor microbiology, 3) resuspension and exposure, 4) current practices and future needs, and 5) sustainability. Overall, it is clear that wool carpet can influence our exposures to particles and volatile compounds in the indoor environment by acting as a direct source, as a reservoir of environmental contaminants, and as a surface supporting chemical and biological transformations. However, the health implications of these processes are not well known, nor how cleaning practices could be optimized to minimize potential negative impacts. Current standards and recommendations focus largely on carpets as a primary source of chemicals and on limiting moisture that would support microbial growth. Future research should consider enhancing knowledge related to the impact of carpet in the indoor environment and how we might improve the design and maintenance of this common material to reduce our exposure to harmful contaminants while retaining the benefits to consumers.
Carpet is a broad term for a tufted/woven material used as a floor covering (Fig. 2). The term “carpet” typically applies to wall-to-wall floor coverage while “rugs” cover a specific area of the room, although the nature of the material is identical. Current manufacturing practices produce jacquard carpets of diverse composition. Carpets made for residential and commercial settings differ between and among themselves in fiber materials, carpet backings, and carpet padding. Of all carpet, over 95% is made of synthetic fibers, including nylon, polyester and olefin [, , , ], and the remainder include natural fibers such as wool. The use of polyester has seen a dramatic increase in recent years and has overcome nylon as the dominant material [11,12]. Residential carpet often has a higher pile height than commercial, where low pile is common due to resistance to crushing in high traffic areas . The tufted/woven loops can remain looped (so-called loop pile), or they can be cut to create vertical strands (so-called cut pile, as in Fig. 2). Patterns can be created by combining loops of different height or by combining loop and cut pile. Carpet density can also be manipulated by changing how closely the different fibers are tufted into the carpet backing. Broadloom covering (created in wide widths such as 12 feet) has historically been common in residences, and both broadloom and tile are common in commercial buildings . Backing in commercial carpets is often based on polyvinyl chloride (PVC) and polyurethane, while residential carpets commonly use latex backing . Carpet padding may be made of fiber, sponge rubber, or urethane foam. Fiber carpet padding, which has a firm feel, could be natural (e.g., animal hair, jute), synthetic (e.g., nylon, olefin), or resonated recycled textile fiber. Urethane bonded foam accounts for over 85% of carpet cushion in the United States . The use of carpet pad underlayment is typical of residential installations, while the use of adhesives for installation predominates in commercial settings.We need to continue to refine our understanding of chemical emissions from carpets into the indoor environment, especially for emerging contaminants. We also need to better understand the chemical reactions occurring on the carpet, including aqueous reactions in water films on porous indoor surfaces. Additionally, work measuring VOC emissions from carpet to characterize new materials and manufacturing processes as they are introduced into the market will continue to be important.
Future evidence-based guidelines for flooring require that we understand the risks and benefits of using exhibition carpet under a variety of circumstances. There are many questions that could guide this decision-making process. Do the benefits of carpet (such as cushioning/prevention of falls, comfort, aesthetics) outweigh the risks (such as exposure to chemicals and biological agents, resuspension of particles)? The answer to this question may differ depending on any given set of circumstances and the risks/benefits of alternative flooring materials. How do other housing systems, such as ventilation, moisture and pest control, and typical cleaning practices, interact with carpeted surfaces? What are the financial and health implications of increased use of carpets of varying types on building maintenance, capital improvements, and overall sustainability? Most importantly, how will improved knowledge affect both consumer behavior and corporate marketing strategies? Ultimately, an improved understanding of the risks and benefits of different flooring materials will allow us to improve health, housing sustainability, and overall societal and economic benefit.Designing carpets that have the ability to improve indoor environmental quality related to dust retention, resuspension, and microbial growth should be an environmental health goal. This goal also needs to involve consumer education on why these properties of carpet are important to the indoor environment and occupant health. Currently, consumers tend to assess the cleanliness of carpet through visual inspection, which may not be an accurate representation of cleanliness as some carpets are designed to appear clean even when they are not. Consumers need to understand the benefits of improvements in carpets for environmental health to warrant purchasing any products that may be developed. To provide this education, we also need a thorough understanding of how carpets impact indoor microbiology and indoor chemistry.
Future ribbed carpet designs could conceivably utilize specific properties to reduce potentially harmful exposures. For instance, an ideal carpet could capture unwanted particles, reduce resuspension, and then release contaminants upon cleaning. Specific target values, such as a certain resuspension rate associated with health outcomes, could help in achieving these goals and could mimic the Green Label Plus™ program. Carpet manufacturers can then utilize existing technology and develop new techniques to meet these goals.
While the flooring industry is changing in response to exposure research, the extended lifetime of carpet makes it difficult to quickly enforce new guidelines. Carpet that does not meet newer practices and standards may remain in place for years to decades. Information must be accessible and understandable to consumers so that informed decisions can be made about sustainability and exposure issues.Carpets are an integral part of our indoor environments. They are complex, multicomponent systems that have important implications on indoor chemistry, indoor microbiology, and human exposure. Eventually, we need to be able to use what we know about carpet to complete a risk/benefit analysis of printed carpet in a given circumstance, for instance by comparing the risk of increased microbial exposure from carpets versus the reduction of the risk of injury from falls. This risk/benefit analysis could also indicate situations where a carpet should be removed or cleaned. This analysis could potentially change with future development of carpets that promote environmental health by reducing resuspension and therefore occupant exposure. Ultimately, this information can lead to better carpet design and improved recommendations for flooring selection in the indoor environment to improve human health.The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government and shall not be used for advertising or product endorsement purposes.