Selection Principles for Hazardous‑Gas Detection and Alarming Instruments
① Clarify detection purposes and select instrument categories In short, hazardous‑gas detection has two objectives: explosion‑risk detection and toxic‑gas detection. Explosion‑risk detection measures combustible‑gas concentration in hazardous locations and gives an alarm upon threshold exceedance to prevent explosions. Toxic‑gas detection monitors toxic‑gas concentration and triggers alarms to protect staff from poisoning. The measuring range for explosion‑risk detection is 0‑100 %LEL, while toxic‑gas detection ranges from zero to tens or hundreds of ppm; there is a substantial difference between them.
There are three typical conditions of hazardous gases on‑site: non‑toxic (low‑toxic) combustible gases, non‑combustible toxic gases, and combustible‑toxic mixed gases. The first two are straightforward: select explosion‑risk detection for the first case and toxic‑gas detection for the second. For the third case, perform toxic‑gas detection if personnel exposure exists; explosion‑risk detection may be adopted if no personnel are exposed. Choose combustible‑gas detection‑alarm instruments for explosion‑risk detection and toxic‑gas detection‑alarm instruments for toxic‑gas detection.
② Define application scenarios and select instrument types (portable or fixed‑type) Fixed‑type detection‑alarm instruments shall be adopted for long‑term leakage monitoring at production or storage posts. Portable (pocket‑size) instruments are used for overhaul inspection, emergency detection, confined‑space entry detection and patrol inspection. An instrument model mainly covers three elements: manufacturer, performance specifications and detection principle.
③ Confirm target measured substances and select optimal instrument model The following principles shall be followed when selecting a model: ‑ The manufacturer shall be reputable with reliable product quality, holding ISO9002 quality‑system certification, CMC production license issued by technical‑supervision authorities, as well as fire‑protection and explosion‑proof certificates. ‑ Performance indexes of the selected model shall comply with national standards GB12358‑90, GB15322‑94, GB16808‑1997 and other relevant specifications. ‑ The detection principle of the instrument shall adapt to target gases and site‑environment conditions.
Overview of hazardous‑gas sensors A hazardous‑gas sensor converts hazardous‑gas concentration in ambient air into electrical signals. The output signals are processed and amplified by electronic circuits. Sensors work under harsh on‑site conditions. Especially for fixed‑type instruments, sensors run continuously for long periods and are subject to constraints of explosion‑proof requirements and power supply capacity, hence stringent requirements are imposed on them. After signal conversion, gas‑concentration readings and alarm functions are realized. Therefore, the sensor is the fundamental and core component of hazardous‑gas detection‑alarm instruments. Its performance determines overall quality and technical specifications of the whole device.
