In confined spaces such as sewers or cellars, the oxygen content in the air may be too high or too low, and it may also contain toxic and harmful gases. It is very dangerous to enter such a confined space rashly. Before we understand how to safely enter these confined spaces, we must first understand why there is insufficient or excessive oxygen in the confined space.
If the oxygen concentration is too low, the human body will become hypoxic. In more serious cases, it may cause the heart, brain and other important organs to die due to lack of oxygen. In fact, when the oxygen detector detects the oxygen content in a confined space, it must not only consider the possible suffocation and shock of the entering personnel when the oxygen concentration is too low, but also consider the possibility of the interaction between oxygen and flammable substances in the confined space when the oxygen concentration is too high. Chemical reactions can cause fires and other situations.
The oxygen content in normal air is about 20.9%, and among other constituent gases, nitrogen accounts for more than 78%, leaving only carbon dioxide, water vapor, carbon monoxide and other trace gases. Therefore, the zero point of an oxygen detector (that is, the displayed concentration of the oxygen detector in a normal environment), the corrected concentration of the oxygen sensor is set to 20.9% or 21.0%.
Most oxygen concentration standards in confined spaces are based on volume concentration. Generally speaking, when the concentration detected by the oxygen sensor is less than 19.5% of the total volume of the gas, we can conclude that there is insufficient oxygen in the current environment. my country's SY/T6458-2000 and GBZ/T205-2009 regulations both stipulate that the excess oxygen concentration is 22%. Therefore, when the oxygen detector reading exceeds the volume concentration of oxygen in the normal environment by 22%, we consider that there is excess oxygen in the current environment. Regardless of whether the test result is too high or too low, an oxygen detector should set a reasonable alarm value to remind personnel that the oxygen concentration in the current environment has reached a level that can pose a threat to human body or environmental safety, so as to make timely and correct processing decisions.
In actual life and work, the oxygen concentration is normal as long as it is around 20.9%. When the oxygen content is lower than the normal content, it indicates that other component gases in the air are abnormal or there are pollutant gases. At this time, even if the reading measured by the oxygen sensor does not reach the dangerous value, the cause of the abnormal oxygen content must be confirmed before the staff can enter the measured environment.