Wednesday, March 20, 2013 Issue 43  

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Emerging Hazard: Mercury-Containing Flooring
by Will Wade

Products such as thermostats, fluorescent light bulbs, and some electrical switches have long been known as potential sources of mercury but recently another mercury-containing product is gaining attention – polyurethane flooring. Some polyurethane or rubber-like floorings manufactured from about 1960 to 1980 contained mercuric acetate. These floors are most often found in sports settings (e.g., gymnasiums, running tracks) but also can be found in industrial plants and hospitals – wherever a cushioned, all weather, non-slip surface would be needed. Some of these floors can also release significant amounts of elemental mercury in the air, which can in turn be absorbed and re-emitted by furnishings and equipment. Additionally, floors abraded during resurfacing or removal may release more mercury than floors that are intact, posing a potential health concern for workers or the public in nearby locations. This article discusses a mercury-containing flooring removal and remediation effort in a school’s gymnasium and the critical components to its success.

Safe Removal of Mercury-Containing Flooring in a School Gymnasium

A school planned to renovate their gymnasium where the flooring was comprised of hardwood on top of a synthetic rubber subfloor. Due to recent attention on mercury-containing flooring, the school was concerned that the synthetic floor in the gym may contain mercury. The school contracted with EH&E to conduct testing and, if necessary, design a remediation plan to ensure the safety of workers and of faculty and students in areas adjacent to the gym.

Assessing Risk

Testing confirmed the presence of significant levels of mercury in the synthetic flooring.  The project schedule demanded that the mercury-containing floor be replaced while the adjacent spaces remained occupied. Although air testing determined that mercury levels were low in the gym before the hardwood floor was removed, it was critical to verify that mercury concentrations could be controlled after the hardwood floor was removed, exposing the rubber flooring and potentially increasing airborne mercury concentrations.

EH&E performed a risk assessment to establish acceptable site-specific thresholds for mercury concentrations in the gym and surrounding areas during renovation, and clearance criteria before the new flooring could be installed. This included reviews of existing literature and guidance values from agencies such as the US Environmental Protection Agency. A critical issue that arose when planning the project was determining whether there would be mercury emissions from the concrete underneath after the mercury-containing flooring was removed, and whether the replacement floor could be installed by workers without safety precautions. There was no available information to answer this question, and it could significantly increase costs and prevent the gym from opening on schedule. To address the issue, EH&E measured mercury emissions from the synthetic and concrete floors and used modeling to predict the mercury levels in the gym after removal of the synthetic and hardwood flooring. Based on the modeling results, EH&E concluded that airborne mercury concentrations could be maintained under the established exposure thresholds with supplemental ventilation in the gym, adjusting existing air handling systems that also serve adjacent spaces to prevent cross-contamination, and implementing engineering controls.  EH&E provided specifications for the controls and ventilation and the flooring removal project moved ahead on schedule.

Monitoring / Verification during Construction

A monitoring plan was then designed to verify that exposures and risk were controlled. Monitoring was conducted in the gym and adjacent spaces during floor removal. During the removal, EH&E’s measurements verified that mercury levels inside the work zone were low, consistent with the modeling predictions, and mercury levels outside the work zone were also low and well within safe levels.

Once the removal of flooring was complete, and prior to installation of the new flooring, testing was conducted to verify mercury concentrations met the target levels established by the risk assessment and modeling. Testing results confirmed the remediation activities were successful and the school was able to proceed with installation of the new flooring.

Careful Planning is Key

The key to safely and successfully managing environmental hazards such as mercury-containing flooring is careful planning upfront. The risk assessment and modeling were integral to the success of the remediation of mercury-containing flooring in the school gym. These steps provided an accurate assessment of the potential risk during all phases of the remediation so appropriate measures could be put in place to ensure the safety of workers and occupants in adjacent spaces. Before remediation activities begin, it is necessary to conduct a risk assessment and exposure modeling to properly assess the potential risk, establish health-protective exposure thresholds, implement engineering controls and worker protection to minimize exposure risk (if necessary), and determine criteria for re-occupancy.

William Wade is a Staff Scientist at EH&E and has managed many environmental risk management projects, focusing on indoor environmental quality and industrial hygiene in workplaces and construction sites. For additional information, contact Will at


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