Mercury Emissions from a Synthetic Gym Floor: Risk-based Assessment, Flux Measurements, Control and Verification during Removal

Increasing studies have shown that certain synthetic floors installed in gymnasiums from the 1960’s to mid-1980’s emit mercury. Synthetic flooring was discovered under hardwood flooring scheduled for replacement in a university gym, and low-level mercury vapor was detected in the gym (median: 38 ng/m³). A controlled pilot study was conducted and found elevated airborne mercury concentrations after removing the hardwood. Concrete below the synthetic floor also emitted mercury. Removal of the flooring needed to be undertaken in a controlled manner while adjacent spaces remained occupied. Due to emissions from concrete, determination needed to be made if the replacement floor could be installed on the existing concrete by workers without safety precautions.

Health-based mercury vapor limits for adjacent occupied spaces (<1,800 ng/m³ - short-term; <1,000 ng/m³ - sustained), targets for post-remediation (<2,500 ng/m³), and for project completion (<750 ng/m³) were established. Controls were implemented (barriers, exhaust ventilation, dust control). Emission rates were measured from the concrete using flux chambers and predicted steady-state mercury concentrations were modeled.

During floor removal, median mercury concentrations were 3,280 ng/m³. Concentrations in adjacent occupied spaces were well within health-based criteria (median: 51 ng/m³).  Following floor removal, median mercury concentrations were 552 ng/m³ in the gym, consistent with predicted concentrations. At project completion, the median concentration was 5 ng/m³, consistent with background.

Mercury emissions from historical synthetic floors remain a concern.  Effective risk-based measures can be implemented to control work and achieve background mercury levels. Flux measurements and modeling can be used to predict exposure concentrations and aid in decision-making.