What CO2 level is dangerous?

At CO2Meter, our own office encountered an actual CO2 incident and we wanted to share our story with others to provide further perspective on what to do should a potential CO2 leak occur and how CO2 monitors serve their purpose in being life-saving equipment.

It’s important to know, that no emergency or medical personnel were dispatched to CO2Meter that morning. No employees were injured. But, thanks to the many leak detectors in our office, the CO2 alert warned our staff of potentially dangerous CO2 levels instantly. And yes, even the “gas detection people” can have an incident.

Here’s what happened.

Our technicians were studying the effects of extremely low temperatures on carbon dioxide sensors. By using dry ice (the solid state of carbon dioxide) they were able to push the temperature of the sensors and the air they were measuring down in order to test changes in accuracy.

After finishing their testing for the day, the techs placed the dry ice samples in the company refrigerator for temporary storage. Bad idea.

The first person to enter the building the next day heard the CO2 alert warning employees of dangerous CO2 levels. All the CO2 detector alarms in the building were signaling a problem. The LCD readout on the alarm nearest the door indicated the CO2 level was 1,500 ppm (parts per million) – safe but noteworthy.

While CO2 levels above 3% (30,000 ppm) are dangerous and would require the building be evacuated, 1,500 ppm only indicated a small problem. However, any CO2 level above 400 ppm in an unoccupied building was still cause for an alarm.

While several rooms showed elevated levels of CO2, none were unsafe to enter. All the outside doors were opened to ventilate the building. But it wasn’t until the first person opened the refrigerator to store their lunch that the CO2 levels jumped up again.

The staff realized it was the dry ice in the refrigerator’s freezer that was off gassing CO2. Our techs hadn’t realized that while the typical temperature in a freezer is 0 degrees Fahrenheit or -18 degrees Celsius, the freezing point of carbon dioxide is -109.2 degrees Fahrenheit, or -78.5 degrees Celsius. The dry ice was melting in the “warm” freezer.

Actually, the term melting isn’t quite accurate. As a solid block of CO2 warms it sublimates, turning directly into gas, rather than melting into a liquid. Other examples of solids that sublimate are iodine, arsenic, naphthalene (what mothballs are made of) and solid air fresheners. While water normally melts into a liquid, it can sublimate in special conditions of low temperature, low humidity and dry winds.

We were all happy that no one was injured and thankful that our devices worked as intended. As it turns out, even “the CO2 experts” can have a leak once in a while.