Considerations to Determine Gas Sensor Positioning

8 Considerations to determine gas sensor positioning

In this guide, we consider 8 points that should be considered for the performance of the gas detection system.

Incorrect gas sensor positioning will result in an ineffective gas detection system. Firstly, it won't protect those who work there and secondly, it won't protect the workplace.

The benefit of installing a gas detection system is to detect dangerous concentrations of hazardous gas. Once set levels are met, the system has the capability to trigger alarms and activate countermeasures such as fan control systems. However, this can only be achieved if the gas sensors have been positioned accurately.

 

1. Leak Source

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.

2. 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.

Gas Density Sensor 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

3. Pressure 

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

4. Air Currents

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

5. 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.

6. 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.

7. 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.

8. 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.

 

What Does Legislation Say?

Whilst there are no specific standards regulating gas sensor positioning, there are however, useful guidance documents:

  • BS EN 60079-29-2-2007 - Guide for selection, installation, use and maintenance of apparatus for the detection and measurement of combustible gases or oxygen.
  • IEC 60079-29-2-2015 - Explosive atmospheres – Part 29-2: Gas detectors – Selection, installation, use and maintenance of detectors for flammable gases and oxygen.

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.

 

Summary

So there you have it, 8 useful points to help with gas sensor positioning.

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.