Testing for Mercury in Poured Rubber Flooring

Jump to: Introduction | Overview | Analysis and Results | Management and Remediation | 2021 Removal Projects | Post Remedial Sampling | Contact | Frequently Asked Questions


As part of its ongoing commitment to Indoor Environmental Quality (IEQ), HCPSS has initiated a project to identify, test, and remediate poured rubber flooring material in school gymnasiums. This type of flooring may be produced with a mercury catalyst that can emit mercury vapors under certain conditions. Four school locations were determined to have this type of flooring. To determine if there is any health risk, air sampling was conducted at each location periodically during the year, because mercury vapor concentrations vary seasonally due to changes in temperature. The results of the preliminary air quality tests taken thus far show that none of the floors tested pose a health risk during normal school operations.

HCPSS removed the flooring during the summer of 2021, while school was not in session. This measure was taken out of an abundance of caution, and not because of any suspected health risk.

It is important to note that the flooring test and mitigation program was initiated as a proactive measure to improve IEQ, as part of HCPSS’ overall commitment to practices that support a healthy environment. No health concerns have been reported, and the sampling/removal of the flooring is not required by federal, state, or local regulations.


HCPSS has identified four facilities that contain a poured rubberized gym flooring. This type of flooring was widely installed in school gymnasiums across the United States from the 1960’s until approximately 2005. Poured rubberized flooring can contain a mercury catalyst to aid in its installation. This catalyst can emit mercury vapor under certain conditions. These emissions can reach levels of concern in some cases, especially where flooring condition has deteriorated and air temperature is elevated and/or lacks dilution through the Heating Ventilation and Air Conditioning (HVAC) system.

After extensively reviewing the construction documents for each school building, HCPSS identified only four locations with poured rubber gymnasium floors:

  • Bollman Bridge Elementary School*
  • Northfield Elementary School*
  • Old Cedar Lane School
  • Waterloo Elementary School*

*rubber floor covered with standard wood flooring at these locations

Analysis and results

At these four school gymnasiums, HCPSS collected and analyzed preliminary air samples at various locations and heights to determine if the flooring emits mercury vapor during normal hours of occupation. While there are no federal or Maryland state regulations or guidelines regarding rubberized gym flooring containing mercury, the sample results were compared to widely-accepted guidelines from the Minnesota Department of Health and New Jersey Department of Health, which indicate that indoor air concentrations below 750 nanograms per cubic meter (ng/m3) are protective of preschool-aged children, and thus also deemed safe for older children and adults.

Preliminary air quality testing has indicated that none of the floors at these school locations pose a health risk during normal school operations, because all samples taken were well below the 750 ng/m3 threshold. Mercury vapor concentrations vary seasonally due to changes in temperature. The results for each season, and the yearly average, are provided in the table below. These results will be updated as additional seasonal data becomes available.

Sample Results
SchoolSummer 2020
Fall 2020
Winter 2021
Spring 2021
Waterloo ES149 - 2060.5 - 307118 - 15045 - 6578 - 182
Old Cedar Lane85 - 11664 - 7753 - 7344 - 15462 - 105
Northfield ES--84 - 49126 - 15355 - 322
Bollman Bridge ES--3 - 540.5 - 332 - 44

Management and Remediation

During the Summer of 2021, HCPSS removed and replaced the flooring out of an abundance of and caution and not because of any suspected health risk. This process took place during the summer of 2021 and was conducted by board-approved abatement contractors, using specialized work practices. The abatement work was overseen by a third-part industrial hygienist. Links to the third-party reports can be found below:

2021 Removal Projects

Post Remedial Sampling

As a follow-up to the rubberized gym flooring removal the Office of the Environment continued to collect seasonal mercury air samples within the gymnasiums. The sampling was conducted to determine if residual mercury vapor (which reportedly can be “trapped” and off-gassed by the concrete slab) was off-gassing vapor at levels above HCPSS’ voluntary action level of 750 nanograms per cubic meter (ng/m3) averaged over the year.

Sample Results (Post Rubber Floor Removal)
SchoolSummer 2022
Fall 2022
Winter 2022
Spring 2022
Waterloo ES35152517162
Old Cedar Lane29219150208167
Northfield ESND (2)36116
Bollman Bridge ES9464316

HCPSS will utilize a contractor to collect final clearance air samples during late Spring/Summer with the ventilation system off to simulate a “worst-case” scenario. Should these samples be below the HCPSS action level, no further monitoring or action will be taken.

This has been completed for Bollman Bridge Elementary and Waterloo Elementary. No mercury vapor was detected within the samples of either gymnasium. No further monitoring or action is planned for these facilities. Sampling at the remaining schools is planned for the Summer of 2024.


Christopher Madden Industrial Hygienist/IEQ Manager, HCPSS Office of the Environment

Frequently Asked Questions

How has HCPSS determined which buildings contain this type of flooring?

Staff in the Office of the Environment carefully reviewed construction documents and/or conducted on-site inspections to identify schools and other locations having poured rubber flooring. Three schools were identified, as well as one former school that is currently used as an office building.

What are the health risks of mercury?

Mercury is a neurotoxin. Health risks can vary significantly depending on the level and length of exposure and other factors such as the age and health of the individual exposed. The effects of mercury exposure can range from severe to none at all. While exposure can occur in various ways, the most common route is through consumption of seafood containing mercury.

What should I do if I/my child has been in the gymnasium?

Based on the air sampling data obtained and compared to guidelines from the Minnesota Department of Health and New Jersey Department of Health, no further action is warranted. If you have further concerns, you are advised to contact your primary care provider. Note that the Howard County Health Department has also reviewed the data collected by HCPSS. If you have further concerns, you are advised to contact your primary care provider.

How did HCPSS test the samples and determine the level of risk?

Indoor air samples were collected in gymnasiums of concern using a real-time mercury vapor analyzer. Air samples were collected on Monday mornings while the HVAC was operating normally to simulate the “worst case scenario” a teacher or student would be expected to encounter. Results were then compared to the Minnesota Department of Health’s action level of 750 ng/m3. The New Jersey Health Department also has a similar action level of 800 ng/m3.

My activity room/weight room has rubber tiles. Is this a concern?

No. Rubber tiles are not poured into place; therefore, a mercury-based catalyst is not needed for installation. Only flooring constructed of a soft rubber material with no seams may potentially be of concern. At HCPSS, this type of flooring is present only in a small number of gymnasiums.