Two of the most common questions that we hear in regards to gas detectors systems (and probably the most difficult to answer) are ‘how many sensors do I need?’ and ‘where should I locate them?’. Unlike other types of safety related detectors, the location and quantity used for gas applications is not clearly defined. You can seek guidance from the standards of your country or particular state, international codes of practice and from regulatory bodies.
Whilst these references are certainly useful, they tend to either be very generic (and, therefore, too general in detail) or application specific (and, therefore, irrelevant to most applications). The placement of your sensors should be determined by following the advice of experts with specialist knowledge of gas dispersion, of the process plant system and the equipment involved, safety, and engineering personnel.
Essentially, sensors should be mounted where gas is most likely to be present. The locations that would require the most protection include around boilers, compressors, pressurised storage tanks, cylinder or pipelines. Areas where leaks are likely to occur include valves, gauges, flanges, T-joints, filling or draining connections and so on. Fortunately, there are a number of considerations that help to determine the sensor locations for your gas detection system.
- To detect gases that are lighter than air (such as methane and ammonia), sensors should be mounted at a high level;
- To detect gases that are heavier than air (such as butane and sulphur dioxide), sensors should be mounted at a low level;
- Think about how escaping substances may behave as a result of natural or forced air currents; mount sensors in ventilation ducts if appropriate;
- Think about the possible damage caused by natural events (such as rain or flooding) when locating sensors;
- If placing a sensor in a hot climate and in direct sun, you will need to use the accompanying sunshade;
- Think about the process conditions, as some heavier gases may rise if released at an elevated temperature and/or under pressure;
- Sensors should be located a little way back from high-pressure parts so that a cloud can form and you can avoid missing a leak;
- Think about how easy the sensor will be to access for functional testing and servicing by technicians;
- Sensors should be installed pointing downwards to ensure that dust or water will not collect on the front and affect readings;
- If using open path infrared devices, make sure that there is no permanent obscuration or blocking; short-term can be accommodated; and
- Ensure that the structures that any sensors are mounted to are sturdy and not susceptible to vibration.
If you are in the process of determining where to mount sensors for your gas detection system, make sure that you seek expert advice. You should also avoid trying to economise by using the minimum number of sensors, as a few extra could make all the different if a gas leak were to occur. We also encourage you to pay heed to the considerations outlined above to ensure that your sensors are mounted appropriately and safely.