by Joseph L. Sbarra, CIH
Certified Industrial Hygienist with > 35 years experience
How Did Mercury Get in Gymnasium Floors?
From the early 1960’s to the mid 1990’s, schools and other commercial facilities installed polyurethane (rubberized) flooring in indoor gymnasiums, cafeterias and outdoor running tracks and field houses.
Polyurethane flooring became popular as it was less expensive than hardwood flooring, is less resistant to damage, and is easier to maintain. Most commonly, the process involved pouring the floor in three parts:
Some manufacturers’ flooring included a compound that contained a form of mercury called phenyl mercuric acetate (PMA), which was used as a catalyst in production. Even today, 30 - 50 years after installation; floors with the PMA catalyst still emit mercury vapors into the air!
What is Mercury?
Mercury is an element; it is a shiny, silvery metal sometimes also called quicksilver.
It is the only metal that is a liquid at room temperature. Mercury gives off vapors at room temperature; the higher the temperature, the more vapors are released. Mercury vapors are colorless and odorless.
Mercury has historically been used in thermometers, barometers, fluorescent light bulbs and dental amalgams (used for filling teeth).
Are Mercury Vapors a Health Concern?
They can be, the effect on a person’s health depends on a several factors including:
Mercury is a poison, it is not a known cancer-causing agent. Mercury is absorbed into the body primarily by breathing the airborne vapors. Exposure to mercury can affect the central nervous system (CNS), which is very sensitive to mercury. Exposure to lower levels of mercury vapors for prolonged periods of time (which is the most likely case with regard to gym floors) can cause non-specific health effects such as:
Most of the effects of mercury resulting from prolonged low level exposure are reversible, once exposure is terminated and the mercury has left your body. 1
What is the Approach to Dealing with Gym Floors?
There is a basic approach that can be applied to gym floors that contain mercury.
The first step is to conduct bulk testing to determine if mercury is even present. If bulk testing results are below 1 ppm, then no further action is needed.
If the bulk testing results are positive, the next step would be to conduct mercury vapor screening to determine airborne mercury levels. This can be done with a handheld mercury vapor meter that has the capability to detect < 300 nanograms of mercury per cubic meter of air (that's a really small amount!).
Based upon the mercury screening results, a Management Plan would need to be developed to ensure that airborne mercury vapor exposure levels remain below recommended limits. A Management Plan should include:
Lastly, a decision needs to be made with regard to Long-term Planning: manage the mercury gym floor in place or remove it. Several factors should be considered, including:
We Have a Polyurethane Floor…What Do We Do Next?
1. Agency for Toxic Substances and Disease Registry, ToxFAQs TM for Metallic Mercury, March 2001.