In modern industrial production and daily life, combustible gas alarm and toxic gas alarm an important safety instruments, not only preventing fire and explosion and poisoning accidents, “the first line of defense”, but also protecting the lives of people and the core of enterprise safety production equipment. This article will be from the technical principle, classification standards, application scenarios, installation and maintenance, regulatory requirements, and future trends, and other aspects of a comprehensive analysis.

Combustible gas alarm: guarding the safety of flammable and explosive places

1. Core Functions and Detection Objects

Combustible gas alarm is mainly used to detect the concentration of flammable and explosive gases in the environment, such as methane (CH4), propane (C3H8), hydrogen (H2), liquefied petroleum gas (LPG), natural gas and so on. When the gas concentration reaches the lower explosive limit (LEL) of the set threshold (usually 10% to 25% of the lower explosive limit), the alarm will sound and light alarms to signal the danger.

2. Working Principle and Technology Classification
l Catalytic Combustion Sensor: Mainstream technology, utilizing combustible gases to generate heat by burning under the action of a catalyst, and determining the concentration by measuring the temperature change. Applicable to most hydrocarbon gases, fast response time, but susceptible to silicon, lead and other compounds poisoning.
l Infrared (NDIR) sensors: through the detection of gas absorption characteristics of infrared light to measure the concentration of anti-neutral toxicity, suitable for complex environments, but the cost is higher.
Semiconductor sensor: high sensitivity but prone to drift, mostly used in civil scenarios.
l Thermal conductivity sensor: Measure the concentration through the difference in thermal conductivity of gas, applicable to hydrogen and other special gases.

3. Application Scenarios and Typical Industries
l Petrochemical industry: refineries, chemical plants, storage tanks, reactor areas;
l Gas industry: natural gas pipelines, gas stations, city gas pipeline network;
l Coal mining industry: methane concentration monitoring in the mine tunnel;
l Industrial Manufacturing: paint spraying booths, solvent storage areas, boiler rooms, etc..
l Public Places: hotel kitchens, gas supply stations, underground garages and so on.

4. Installation and Configuration Points
l Installation Height: It is decided according to the density of gas. The gas lighter than air (such as methane) is installed at a high place, and the gas heavier than air (such as propane) is installed at 30-60cm above the ground.
l Coverage: the protection radius of a single detector is usually 7.5-15 meters, which should be reasonably distributed according to the area of the place.
l Explosion-proof level: explosion-proof alarms must be used in explosion-hazardous areas (e.g., Ex d IIC T6 level);
l Linkage function: it can be connected with fans, solenoid valves and other equipment to realize automatic ventilation or cut off the gas source.

5. Maintenance and calibration
l Regular calibration: calibrate with standard gas (such as methane, propane) at least every six months;
l Fault checking: test the alarm function, self-test function and check the status of the sensor regularly;
l Environmental protection: avoid high temperature, high humidity, corrosive gas environment, and clean up dust on the surface of the sensor regularly;
l Lifespan management: Catalytic combustion sensors have a life span of 3-5 years in general, and infrared sensors can last for more than 10 years. Lifespan management: Catalytic combustion sensors generally have a lifespan of 3 to 5 years, while infrared sensors can reach 10 years.
6. Typical case study
a chemical plant tank area due to valve leakage caused by propylene concentration rise, a combustible gas alarm in the concentration of LEL 20% triggered an alarm, automatically start the fan and cut off the feed, to avoid a major explosion.

Toxic gas alarm: the silent “life guardian”

1. Detecting objects and hazards
Toxic gas alarm mainly detects hydrogen sulfide (H2S), carbon monoxide (CO), ammonia (NH3), chlorine (Cl2), hydrogen cyanide (HCN) and other toxic gases. Even low concentrations of these gases can lead to serious consequences such as dizziness, asphyxiation, and death. For example, a concentration of 50 ppm of H2S can be fatal in a short time.
2. Technical Principles and Sensor Types
l Electrochemical Sensors: Mainstream technology, measuring gas concentration through electrochemical reaction with high sensitivity and better selectivity. For example, CO sensor produces a current change through an oxidation reaction;
l PID photoionization sensor: suitable for volatile organic compounds (VOCs) detection;
Infrared (NDIR) sensor: used for CO2, SO2, and other specific gases;
Metal Oxide Semiconductor Sensor: mostly used for civil low-concentration detection.
3. Application Scenarios and Special Requirements
l Chemical plants: desulfurization devices involving hydrogen sulfide, ammonia refrigeration plant;
l Wastewater treatment plants: anaerobic tanks, sludge treatment areas;
l Mines and tunnels: hydrogen sulfide, CO monitoring;
l Laboratories: toxic chemical storage and use areas;
l Pharmaceutical industry: organic solvents, toxic intermediate products monitoring.
4. Installation and Configuration Precautions
l Gas diffusion characteristics: for heavier-than-air gases (such as H2S), the detector should be installed close to the ground;
l Multi-point monitoring: the detector is arranged according to the wind direction and the diffusion path of the gas;
l Personal protection linkage: the high concentration area needs to be linked with the escape respirator and the emergency shower facilities;
l Low concentration alarm: some of the toxic gases need to be set up with a “warning threshold” (e.g., a warning threshold). Low concentration alarm: some toxic gases need to set the “warning threshold” (e.g., 1ppm H2S) to indicate the risk in advance.
5. Maintenance and calibration of special
l Zero drift: electrochemical sensors are susceptible to environmental influences, and need to be adjusted to zero regularly in clean air;
l Cross-interference: some sensors are sensitive to other gases (e.g., the CO sensor responds to H₂), and need to pay attention to the interference of the coexisting gases;
l Sensor life: the life span of electrochemical sensors is usually 1-2 years, and they need to be replaced promptly;
l Toxicity test: use standard toxic gases to carry out calibration, and pay attention to safety protection. Pay attention to safety protection.
6. Typical accident warning
A sewage pumping station, due to dredging operations, did not activate the toxic gas alarm, resulting in workers inhaling high concentrations of H2S, highlighting the importance of equipment maintenance and the operation process specification.

Alarm classification and standards

1. According to the installation mode classification
l fixed alarm: long-term installation in dangerous places, real-time monitoring;
l portable alarm: inspection, temporary operations, such as a hand-held detector;
l wireless alarm system: through a wireless network to achieve multi-point monitoring and remote monitoring. 2.

2. Explosion-proof and certification standards
l International certification: ATEX (European Union), IECEx (International Electrotechnical Commission), UL (United States);
l Domestic certifications: Ex explosion-proof certificates, CMC license for measuring instruments, CPA certification;
l SIL level: Safety Integrity Level (SIL1 ~ SIL3), for high-risk situations.
3. National Standards and Regulatory Requirements
l Chinese Standards: GB 12358 “General Technical Requirements for Environmental Gas Detection and Alarm Apparatus in Workplaces”, GB 50493 “Design Standards for Detection and Alarm of Combustible and Toxic Gases in Petrochemical Industry”;
l Regulatory Requirements: The Work Safety Law, Fire Safety Law, etc., explicitly require that high-risk places must be equipped with gas detection and alarm devices.

Intelligent and Future Development Trends

1. Internet of Things (IoT) integration
Remote monitoring, data recording and analysis through the cloud platform, combined with GIS maps to show the distribution of gas concentration in real time;
2. AI algorithms
Using machine learning to identify abnormal concentration trends, early warning.
3. All-in-one sensors
A single device integrates multiple gas detection functions, reducing costs.
4. Wireless self-organizing network
No wiring required for rapid deployment. Rapid deployment, suitable for temporary places.
5. Miniaturization and low power consumption
Chip-size sensors and battery technology to promote the long battery life of portable devices;
6. Virtual Reality (VR) training
Simulation of gas leakage scenarios to enhance emergency response capabilities.

Use and emergency response precautions

1. Alarm hierarchy response:
l first-level alarm: early warning, check the source of leakage, start ventilation;
l second-level alarm: immediate evacuation, cut off the source of danger, start the emergency response plan;
l third-level alarm: the concentration continues to rise, notify the fire and other professional rescue.
2. False alarm processing:
l Check the environmental factors (such as steam, fume interference);
l Confirm whether the sensor is faulty or the calibration is out of date;
l Avoid misoperation leading to alarm.
3. Personnel training:
Regular training on gas detection knowledge and simulation drills on emergency escape procedures.

Conclusion

Combustible gas alarm and toxic gas alarm is not only a “safety instrument”, but also a “life monitor”. Its reliability is directly related to production safety and personnel health. With the integration of industrial intelligence and Internet of Things technology, gas detection equipment is moving towards a more accurate, more intelligent and more convenient direction. But no matter how the technology progresses, standardized installation, regular maintenance, strict management is always the basis for ensuring its effectiveness. Only by fully recognizing its importance can we build a strong safety defense and prevent it from happening in the first place.