Gas detectors (CO, CO2, O2, multi-gas)

Gas detectors (CO, CO2, O2, multi-gas) are instruments for measuring the concentration of gases in the air. They are used for safety in confined spaces, for monitoring workplace air quality, for incident alarms, for industrial process control and for compliance with safety regulations. The gases most frequently measured are: CO (carbon monoxide, a toxic gas produced by incomplete combustion), CO2 (carbon dioxide, which builds up in crowded enclosed spaces or in process environments), O2 (oxygen, checking for deficiency in confined spaces or excess in industrial processes), H2S (hydrogen sulfide, toxic in oil & gas and sewers) and LEL (combustible gases).

Personal detectors (single-gas and multi-gas)

Personal detectors are wearable devices (clipped to a pocket or belt) that continuously monitor the air the worker breathes, with audible, visual and vibrating alarms if safety thresholds are exceeded. Single-gas detectors measure one gas (generally CO for civil applications, H2S for oil & gas, O2 for confined spaces); multi-gas units combine 4-5 sensors in a single device (the typical configuration being O2, LEL, CO and H2S – the four gases most common in confined spaces). Battery life is typically 8-24 working hours, or 1-3 years for disposable models. They are personal safety devices (category III PPE, certified for ATEX explosive atmospheres).

Detectors for confined spaces

Entry into confined spaces (tanks, sewers, cisterns, tunnels, manholes) requires the atmosphere to be checked beforehand for the absence of toxic or flammable gases and for oxygen deficiency or excess. Detectors fitted with a suction pump and a flexible probe allow the air to be drawn from the space from outside, before the worker enters (the pre-entry check procedure). The acceptance thresholds are: O2 between 19.5% and 23.5%; LEL < 10%; CO < 25 ppm; H2S < 10 ppm. Above these values entry is prohibited or requires self-contained breathing apparatus. In Italy, Legislative Decree 81/2008 governs the safety procedures.

IAQ detectors for indoor air quality

For indoor air quality (IAQ) applications in offices, schools, hospitals, nurseries, gyms and restaurants, multi-parameter detectors are used that measure: CO2 (an indicator of occupancy and ventilation – above 1000 ppm it indicates insufficient ventilation); VOCs (Volatile Organic Compounds – from building materials, furniture and cleaning products); PM2.5 and PM10 particulate; and temperature and relative humidity for comfort. They are used for environmental audits, for wellbeing certifications (WELL, BREEAM, LEED), for health inspections and for post-COVID monitoring of public and school buildings.

Sensors and technologies

The sensors used are: electrochemical for CO, H2S, O2, NO2, SO2 and NH3 (compact, selective, with a service life of 1-3 years); NDIR (Non-Dispersive InfraRed) for CO2 and hydrocarbons (virtually unlimited life, excellent stability); PID (Photo Ionization Detector) for total VOCs (ppb sensitivity, excellent for VOCs); catalytic for combustible gases (LEL); semiconductor for general applications; and laser sensors specific to methane. Each sensor has its own characteristics of sensitivity, selectivity, range, response time and service life.

Reference standards

The main standards are: EN 50543 (CO/CO2 detectors for residential and similar use); EN 60079-29 (detectors for explosive atmospheres); EN 45544 (toxic gases); in Italy, Legislative Decree 81/2008 (workplace safety, confined spaces); ISO 16000 (indoor air quality – a series of standards); UNI EN 13205 (occupational exposure to airborne pollutants); UNI 11254 (procedure for IAQ surveys in school environments). Periodic calibration with certified gas cylinders is essential (typically every 6-12 months) to guarantee that safety-critical detectors work correctly.

Selection criteria

The choice of detector depends on: the gas to be monitored; the application (personal, fixed, IAQ, confined spaces); the alarm thresholds; the safety certifications required (ATEX, MED for marine use, IECEx for explosive zones); the display and alarm signalling; battery life; compliance with the applicable regulations; integration with remote management systems and data archiving for audits; and the calibration service and sensor replacement at end of life.