% instead of PPM
If you just learned what ppm stands for, it might be confusing that the alarm world talks about %. There is a reason, however. Since alarms usually work with high levels of concentration, ppm figures become too large to handle.
100% = 1,000,000 ppm
1% = 10,000 ppm
So, how do we translate percentage to the alarm world?
Fresh air contains 0.04% CO₂. When CO₂ rises to 1.5% (15,000 ppm), your heart rate may increase, and at 4% (40,000ppm) you are in immediate danger.