Tire-Derived Flooring Chemical Emissions Study and Indoor Reference Exposure Levels (iRELs)

Building Materials Emissions Study Background

The California Integrated Waste Management Board (CIWMB, now know as CalRecycle) sponsored the Building Materials Emissions Study or BMES (California Department of Health Services, 2003) to measure the chemical emissions from building materials. The BMES included measurements of 77 separate materials in 11 different categories. The emissions study tested 11 rubber flooring products. Some of these chemicals appear on the Office of Environment Health Hazard Assessment’s (OEHHA) Reference Exposure Lists, The Proposition 65 list or the Toxic Air Contaminants (TAC) list. These Lists establish toxic dose limits, but the latter does not establish exposure concentration limits.

The BMES found Tire-Derived Rubber (TDR) flooring products to emit a substantial amount of chemicals with no established reference exposure levels for health protections, as well as a large number of small peaks of volatile organic compound (VOC) that could not be identified.  The BMES authors concluded (in 2003) that “further refinement and testing of rubber-based… productsare necessary before these products can be promoted for wide use in most indoor environments.”  In addition, the emissions study raised questions about how long certain chemicals would off-gas from these products over time.

Indoor Reference Exposure Levels and Tire-Derived Rubber Flooring Chemical Emissions Study

In 2005, CIWMB sponsored the follow up to the BMES which was broken into two main pieces.  The first piece was the development of Indoor Reference Exposure Levels (iRELs) with OEHHA for four chemicals previously found in tire-derived materials that had sufficient toxicity data.  The second component was the Tire-Derived Flooring Chemicals Emissions Study, was was subcontracted to Public Health Institute (now California Department of Public Health) to perform chemical emission testing on tire-derived and new rubber flooring products.

The iREL is an air concentration that would be below the level at which health effects would not be anticipated to occur in the general population with repeated 8-hour exposures.  OEHHA developed iRELs for: Ethylene Glycol mono-N-butyl ether, N-Methyl-3-pyrrolidinone, naphthalene, and 1, 2, 4-TriMethylbenzene.

The California Department of Public Health’s (CDPH) Indoor Air Quality Lab performed the chemical emissions testing of TDR and NR (new rubber) flooring products.  A variety of TDR and NR flooring products were acquired directly from manufacturers shortly after productions, including replicate samples manufactured in different production lots.  Specimens were tested using CHDP’s Standard Practice 14-day test period (as in BMES); testing of individual samples was continued for three months.  The protocol included sample conditioning for 10 days, followed by VOC testing after four days to yield the “14-day” emission factors.  The protocol was “extended” and VOC emission tests also were conducted at 28, 60, and 90 days.  There was limited success in identifying previously unresolved GC/MS peaks, although they were able to group many compounds into chemical classes.  Low-power optical microscopy was used to record surface characteristics of each product.

The Final Report can be downloaded here.

Study Results

In February 2011 OEHHA and CDPH presented the Chemical Emissions Study results at CalRecycle’s monthly public meeting. Results show that TDR and NR flooring products emit a myriad of VOC chemicals, and their release is not uniform among the different  products. In general, rubber flooring products were found to emit a range of VOCs at different rates due to variations in material properties, and thickness. Several TDR flooring products emitted high rates of VOCs over the tested period, although chemicals of known health concern were at low levels or absent in most products.  Xylene, butylated hyroxytoluene, ethylbenzene, toluene, formaldehyde, and acetaldehyde were found in a range of products.  Benzene and carbon disulfide were above the health threshold in one or two samples.

Conclusions and Recommendations

As Noted in the 2003 BMES, the Chemical Emissions Study findings showed that both TDR and NR flooring products emit a myriad of VOCs.  A minority of products released excessive amounts of chemicals.  TDR flooring products designated for interior-only use are generally lower emitting; exterior products were frequently “super VOC emitters.”  NR flooring products in this study emitted higher amounts of some chemicals than TDR products.  Indoor modeling for these products emission rates indicated potential exposures near the cREL for acetalaldehyde, benzene, formaldehyde, naphthalene, toluene, and xylene at 14 days.  Potential exposures were generally not high among the interior-only products tested, and emission rates, for most of these chemicals appear to decrease by the 28-day tests.

  1. Subject to VOC screening of specific products under CDPH Section 01350, TDR and NR flooring may be acceptable for indoor use, although products designated for exterior or exterior-interior use should generally be avoided (indoors).
  2. TDR and NR flooring can emit high levels of chemicals that do not have health-based guidelines or standards, and occasionally, some major constituents are not readily identifiable by routine analytical methods. Because of these characteristics, consideration should be given to setting an allowable limit for “total” VOC emissions for rubber flooring (both TDR and NR) to be used indoors (e.g., as used in Greenguard IAQ certifications), as a supplement to CDPH Section 01350 VOC screening and acceptance criteria.
  3. Pre-occupancy flush out (or off-site pre-conditioning) is appropriate when TDR and NR flooring products are used indoors. Data suggests that most chemicals emissions are substantially reduced after ~28 days; however, substantial emissions of several compounds remained through the 90-day conditioning period. This raises concerns about “new” rubber flooring products impacts (e.g., sensory) persisting past installation.

The inconsistent presence of a few chemicals (e.g., benzene) suggests occasional reliability problems for crumb rubber or processing chemicals sources. Manufacturers should screen sources of rubber and solvents used in rubber-flooring manufacturing for contaminants that are not essential to production.

For more information contact: Office of Public Affairs, opa@calrecycle.ca.gov