News and Events

Hidden Hazard in Plain Sight: Many School Gym Floors Contain Elemental Mercury

posted 07.31.2019

Gym floor

Providing safe and secure spaces for our community spaces is just one of the reason’s our environmental professionals come to work every day. So, when just prior to the start of a new school year a concerned school district preparing to renovate two older, elementary school gym floors needed assistance to safely remove flooring material, we were glad to help.

School districts across the nation often install rubberized, polyurethane floors in school gymnasiums. This spongy (cushioned) flooring material is resilient; resisting water damage and absorbing the shock of pounding of feet and tumbling bodies which reduces the chance of injury. However, many of these multi-purpose floors have a dangerous hazard hidden in plain sight. The US Environmental Protection Agency (EPA) reports that certain polyurethane flooring materials installed since 1962 actually contain mercury. The inhalation of mercury vapor can cause damage to the nervous, digestive and immune systems, lungs, and kidneys.  Health risks from mercury are greater in younger children or the fetus. Multiple manufacturers produced these floors and marketed to schools as well as industrial plants, hospitals, zoos, and other applications where water-resistant, softer floors would be beneficial.

The polyurethane floors are typically “poured” in place using two chemical resins that form a durable surface. Mercury was added as the catalyst to allow the two resins to react and solidify. The mercury catalyst is not completely bound in the flooring matrix, meaning some floors can emit mercury vapors that are absorbed and then re-emitted by furnishings and equipment such as floor and wall mats, porous fabrics, and even basketballs. As the floors age and deteriorate, mercury vapor release can increase.  Mercury vapor emitted by the floors, may be at high enough levels to be considered a health hazard. Unfortunately, the floors may also contain unbound mercury that exceeds the EPAs Resource Conservation and Recovery Act (RCRA) limits and can be classified as hazardous waste. Hazardous waste must be removed and disposed in accordance with federal laws or substantial penalties can be levied against the building owner.

At Terracon, we recommend to our clients with polyurethane floors, a process to collect samples before disposing of them. The samples are submitted for the toxic characteristic leaching procedure (TCLP) to determine if mercury is present. If the TCLP test for the floors exceeds RCRA standards, the material must be disposed as hazardous waste.  Additionally, we recommend air quality sampling be conducted to determine if students and staff are being exposed to mercury vapors in gymnasiums or adjacent areas.

In the case above, Terracon determined that the two rubberized gym floors did contain mercury, and that that the polymeric floor significantly exceeded the RCRA TCLP threshold. Our lab test indicated that the material must be treated as hazardous waste and abated in a safe manner.

Our team immediately prepared abatement specifications for both schools (gyms) including engineering controls to protect the school’s indoor environments. Abatement of the floors was conducted in negatively pressurized containments by workers trained to handle hazardous materials after a competitive bid process managed by Terracon for the school district. Terracon provided onsite daily consulting and air quality monitoring for mercury within the schools to make sure mercury vapors were not contaminating adjacent indoor areas. After final removal of the floors, Terracon conducted final air clearance sampling before containment structures were allowed to be removed. We also monitored the abatement workers for mercury exposure during the project to ensure OSHA compliance and that the workers had the correct respiratory protection. The project was successfully completed just days before the start of the new school year.

The concerned District agreed with our recommendation to test gym floors in 27 other schools. Five more schools were found to have mercury-containing materials, causing additional safety concern as there was not enough time to conduct the abatement before the start of the school year. Terracon developed a routine air sampling program to monitor mercury vapor throughout the school year in the five gyms. The air sampling program made sure students and staff were not exposed to mercury at unsafe levels and a plan for future abatement was developed. The floors in these five schools were abated the following summer.

Presented with possible mercury exposure in school gyms, Terracon stepped forward as the school district’s trusted advisor and showed our commitment to being responsive, resourceful, and reliable and a partner in keeping the District’s students and staff safe.


Robert Garrison is a Senior Associate at Industrial Hygiene Department Manager in Terracon’s DFW Metro Office.  He has more than 35 years’ experience in the field of Indoor Environmental Quality (IEQ), Microbial Investigation/Remediation and Industrial Hygiene.  Robert has managed multiple, large and diverse projects such as proactive IEQ evaluations for national clients, asbestos inspections for transportation clients nationwide, and has provided environmental consulting for numerous school districts in North Texas.