Advice on Selecting Fixed Gas Detection Systems

You’ve realised the benefits of installing a fixed gas detection system and now you’re faced with the challenge of working out which type of product / system is right for you.

There are major differences in product specification, functionality, enhanced features and the potential value gas detection systems can offer.

Every site is unique in design, needs and processes undertaken so the following factors must be considered to help narrow down the search for the right fixed gas detection system.

Factors to consider are:

  • Site risks
  • Prime objective
  • Source of gas and the types of gas to be detected
  • Gas properties and dispersion
  • Location & environmental conditions
  • Sensor positioning
  • Service & calibration

Understand the site risks

Whilst considering which type of fixed gas detection equipment to buy, a site risk assessment needs to be conducted to identify potential hazards in both manned and unmanned areas of the site.

Any company employing staff has the obligation to conduct risk assessments to identify potential hazards and these can include potential gas, vapour or oxygen deficiency risks.

Identify the prime objective

Whether your site is a chemical plant, an industrial manufacturing warehouse, or an oil and gas rig, identifying the primary objective for each process being undertaken may be required for Health and Safety management records. Some sites may be satisfied with reporting alarm events and therefore no data storage is required whereas others will continuously data log for research purposes.

You may need to identify the gases being detected, remote alarm notification or event data logging and or reporting. Another factor impacting on the need for enhanced reporting functions might be regulatory compliance or a condition of insurance.

Discover gas source and the gases to be detected

The gases to be detected should be identified by the risk assessment, however experienced gas detection equipment suppliers are often able to help in this process, based on their experience of similar applications. However, it is the end-user’s responsibility to identify all potential hazards.

It is also essential to identify the potential source of a toxic or flammable gas release. 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. By identifying the source of a potential leak, it helps determine the number and location of detectors required for a fixed gas detection system.

Consider the environmental conditions

The performance, accuracy and reliability of any gas detection equipment will be affected by the environmental conditions it is subjected to. For example a wastewater treatment plant will be affected by seasonal temperatures, humidity and the change of wind direction. The location and type of sensor installation all have a direct bearing on the type of equipment that should be selected.

Fixed-point detectors are very effective in stable conditions but can be compromised in harsh or challenging situations. On an oil and gas platform, weather conditions can quickly change. A gust of wind may dispel any leaking gas and blow it away from the gas detectors. In these conditions, by the time a gas cloud triggers an alarm if at all, it could potentially reach a highly explosive level.

Gas does not need to come into contact with the acoustic detector as it has to with fixed-point detectors. The acoustic detector responds to the source of the gas (as a frequency), instead of the gas itself.

Considerations to Help Determine Gas Sensor Positioning

The position of a gas sensor should be considered carefully by those installing fixed gas detection sensors. Fixed sensors should be positioned to detect any accumulation of gas and trigger an output before it creates a serious hazard.

Weight of Gas - All gases have different molecular weights which mean that some gases are heavier than others which means that sensors need to be positioned at varying heights.

Pressure - If gas is released under pressure or high temperature, gas may rise rather than fall. 

Air Currents - Natural or forced air currents may cause gas to behave differently. An airflow test can be carried out using non-hazardous smoke test tubes to allow the assessor to visually monitor airflow currents within the workplace prior to installation.

Climate - 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.

Gas Sensor Orientation - Some gas sensors must be positioned using a certain orientation. For example, 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.

Obstacles - Before any wiring is laid, consider the length of cabling required and the obstacles that need to be avoided between the gas sensor transmitter, the gas controller and building management systems. We can overcome this with the introduction of wireless communications. When fitting open path IR devices, it is important to ensure that there are no potential obstacles blocking the IR beam.

Service and Calibration

Routine maintenance is another important consideration which can affect overall costs of maintaining a fixed gas detection system.

Frequency of maintenance – Catalytic beads do not provide fail-to-safety operation and therefore can require a high frequency of routine maintenance. However infrared tends to have a higher initial purchase price, but may require less routine maintenance.

Access - Fixed gas sensors that are positioned high may require a ladder or temporary platform for access which can increase service visit time and costs.

In-house resource – If in-house resource is absent to undertake routine maintenance, budgeting for a third party maintenance company is an important factor in selecting the right equipment.

Continued protection during servicing - Failure or removal for maintenance of an individual gas sensor should not compromise the safety of the area being monitored. Duplication of sensors and control systems may be required for continuous monitoring and to prevent false alarms.

Smart sensors - Installation of the smart gas sensor is a simple plug-and-play action which presents a time saving for each device. Sometimes these sensors are pre-calibrated too. Simply attach the specific toxic or combustible sensor to the gas detector head and it automatically determines the type of gas to be detected.

Enhanced Product Functionality

‘You get what you pay for’. Enhanced product features can deliver better functionality but often cost more. However, by comparing against the cost of service man hours, costs can be recouped over time.

Local display - Gas sensor transmitters with a local display may be preferred as it gives engineers an indication of alarm status, gas levels, and faults. This is a useful addition for maintenance engineers for quickly recognising issues or carrying out calibration.

Communications – The addition of HART® presents many potential benefits for assisting with planned and scheduled maintenance, improving time efficiency and ensuring maximum equipment uptime. It can also deliver communications between a gas sensor transmitter and a control system without the need for additional cabling which can provide a huge cost saving.