Information Deficiencies in the Selection of Hazardous Gas Detectors
Special attention shall be paid to oxygen in industrial applications, especially in confined spaces. Generally speaking, oxygen concentration above 23.5% is defined as oxygen enrichment (oxygen excess), which carries a high risk of explosion; oxygen concentration below 19.5% is regarded as oxygen deficiency (hypoxia), which may cause suffocation, coma and even fatal accidents for on-site personnel. The normal oxygen concentration in the atmosphere is approximately 20.9%. The oxygen detector adopts an electrochemical sensor as its core sensing component.
Existing Problems in the Selection of Hazardous Gas Detectors
Due to historical factors and insufficient professional awareness, there are prominent problems in the selection of gas detection instruments in China, which are summarized as follows: ① More emphasis is placed on the detection of flammable gases than toxic gases. ② More attention is paid to gases causing acute poisoning than those leading to chronic poisoning.
Driven by painful lessons from explosion accidents caused by flammable gas leaks, enterprises attach great importance to flammable gas monitoring. In petrochemical and chemical plants, the vast majority of hazardous gas detectors deployed are LEL (Lower Explosive Limit) detectors. Nevertheless, relying solely on LEL detectors is far from sufficient to fully safeguard the personal safety and health of staff.
It is true that most volatile hazardous substances are flammable gases, yet catalytic combustion LEL detectors are not the optimal solution for all flammable gas measurements. Such instruments are calibrated specifically for methane and deliver poor detection performance for other compounds. As a result, the minimum detectable concentration of flammable gases (excluding methane) by LEL detectors is far higher than their occupational exposure limits.
For example, it is extremely risky to rely only on LEL detectors for toxic and hazardous gases such as benzene and ammonia. The lower explosive limit of benzene is 1.2%, with a correction factor of 2.51 on methane-calibrated LEL detectors. This means the reading displayed by the LEL device only accounts for 40% of benzene's actual concentration. The lowest alarm threshold of benzene on the LEL detector is calculated as: 10%LEL = 10% × 1.2% × 2.51 = 3.0×10⁻³ This value is nearly 600 times higher than benzene's permissible exposure limit of 5×10⁻⁶. Similarly, the alarm concentration of ammonia measured by an LEL detector is 1.5×10⁻², around 600 times its allowable concentration of 2.5×10⁻⁵. Therefore, selecting dedicated toxic gas detectors according to the target measured gas delivers far higher safety and accuracy than simply using universal LEL detectors.
In addition, current practices focus heavily on gases that trigger acute poisoning, such as hydrogen sulfide and hydrocyanic acid, while insufficient attention is given to substances causing chronic poisoning, including aromatic hydrocarbons and alcohols. In fact, the latter pose equivalent severe threats to workers' safety and long-term health, potentially inducing cancer and other latent illnesses that impair life quality and lifespan. Apart from cognitive gaps, the historical shortage of qualified detectors capable of tracing low-concentration organic vapors in the market is another major contributing factor to this issue.
