Just What is a Part Per Million of Sterilant Gas?

As you know, here at ChemDAQ we produce toxic gas monitoring systems with the safety of workers as our first priority. You are also probably familiar with the current regulations pertaining to chemical sterilants. For example, the OSHA Permissible Exposure Limits (PELs) for Ethylene Oxide (EtO) and Hydrogen Peroxide (H2O2), two common sterilant gases, are 1.0 part per million (ppm). For Ozone, the PEL is 0.1ppm. In dealing with gas, which has an incredible amount of particles, it is difficult to understand just what a part per million really is. So to make it a little easier to comprehend, we’ve come up with a few analogies:

A single ppm is…
The first step of a 380 mile walk.
One hair on your head and on the head of nine of your friends.
One second out of 11.6 days.
One penny out of 19 – 5 gallon water jugs filled with pennies.
One drop of water (.05ml) in a 13 gallon tank.

Now that you have an idea of just how small one ppm really is, consider this. The average sterilizer uses several percent by volume of the active sterilant gas in the chamber. Just one percent of that volume is equivalent to ~10,000ppm. Therefore, even the smallest leak or simply the off gassing of sterilized equipment could release an amount of toxic gas into the breathing zone capable of significantly affecting the health of those exposed. Without a continuous monitoring system, workers wouldn’t know that they were being exposed until the concentrations of gas in the air have reached levels far above the PELs, thus putting their health in jeopardy.