Considerations for Positioning Gas Sensors 

Where Should I Locate My Gas Sensors? 

The objective use of a fixed gas detection system is to help maintain safety within the workplace. The benefit of installing a gas detection system to detect dangerous concentrations of hazardous gas is that it can trigger alarms and activate countermeasures such as fan control systems but this can only be achieved through the reliability of the gas detection system and how gas sensors have been positioned.

Incorrect gas sensor positioning will result in an ineffective gas detection system.

The optimum method of gas detection is to place the gas sensors as close as possible to a potential gas leak source. Leaks are most likely to arise from pumps, valves, flanges, joints and shut-off devices.

If such locations cannot be easily identified, gas sensors need to be installed over the entire hazardous area. It is essential that the target gas can always reach the gas sensor at operational conditions within a realistic time interval.

7 considerations to help determine gas sensor position

1. Weight of Gas 

The most common flammable gases which are considerably lighter than air: Hydrogen (H2), Ammonia (NH3), and Methane (CH4). Sensors for these gases should be mounted at a high level.

Heavier than air gases: Butane (C4H10) and Sulphur Dioxide (SO2), and vapours of flammable liquids require gas sensors to be installed at a low level as they flow downwards as long as they are not disturbed by air convection.

GasDensitySensor Mounting

CO2

1.5

Breathing Zone or Lower

O2

1.1

Breathing Zone (4-6 Feet)

NH3

0.6

Breathing Zone and High

Cl2

2.5

Within 6 inches of Floor

ClO2

2.3

Within 6 inches of Floor

CH4

0.6

Within 12 inches of Ceiling

H2S

1.2

Breathing Zone (4-6 Feet)

O3

1.6

Breathing Zone or Lower

SO2

2.3

Near "Potential Leaks" or Breathing Zone

2. Pressure 

Considerations must be paid to process conditions. If gas is released under pressure or high temperature, gas may rise rather than fall. 

3. Air Currents 

Natural or forced air currents may cause gas to behave differently. Gas sensors should be positioned in ventilation ducts if appropriate.

4. Climate

Gas sensors should be installed pointing downwards to prevent dust and water collecting and entering the gas sensor.

When mounting gas detectors outside, consider the possible damage caused by rain or flooding. Splash-proof weather guards will protect gas sensors to a degree but gas sensor positioning must be considered for potential large volumes of water.

Use a gas detector sunshade if locating a gas detector in a hot climate and in direct sun.

5. Gas Sensor Orientation 

Some gas sensors must be positioned using a certain orientation. The catalytic bead sensor must be installed vertically with the gas sensor pointing towards the ground. If the gas sensor is not mounted in this way, then the gas sensor may not work correctly.

6. Obstacles 

When fitting open path IR devices, it is important to ensure that there are no potential obstacles blocking the IR beam.

Before any wiring is laid, consider the length of cabling required and the obstacles that need to be avoided between the gas sensor head gas controller and building management systems. We can overcome this with the introduction of wireless communications.

7. Service and Calibration 

Consider ease of access for service and calibration. Gas sensors that are positioned high may require a temporary platform or ladder for access which can increase service visit time and costs.

Useful to know

The local conditions of the individual hazardous areas are so very different that there are no regulatory standards where to place a sensor, but useful guidelines exist (e.g. EN 60079-29-2).

The placement of gas sensors should always be determined with the advice of an industry expert who has experience in sensor placement, gas dispersion and supported by the assistance of local operators who understand the workflow and operations of the plant.

If you need some help identifying the most suitable position of gas detection sensors, contact a1-cbiss. We have experienced gas detection engineers who are happy to conduct an on-site survey which will identify where gas sensors should be positioned and we can suggest how many gas detectors are required.

a1-cbiss have over 25 years of experience specialising in the design, installation, commissioning and service of fixed gas detection systems. To find out more about the fixed gas detection range that a1-cbiss can offer, contact us below.