Important Fundamentals of Flame and Gas Detection

 Flame and gas detection systems are essential to the protection of people and property in a wide range of industries. Oil refineries and processing plants utilize or produce many hazardous, combustible, and toxic gases. In addition, the processes involved in each industry can produce non-toxic gases which, when accumulated in high concentrations, deplete oxygen and create hazardous conditions for personnel who occupy the area without proper protection. Power plants utilize hydrogen as a coolant, and being highly combustible, hydrogen leaks could be fatal as they can cause explosions and fires. The chemical industry handles many hazardous substances, mining and mineral processing involves methane, carbon monoxide, hydrogen sulfide, and hydrogen cyanide that require continuous monitoring, and pulp and paper mills have processes that either utilize toxic gases or whose by-products are toxic. All of these industries require the correct methods of flame and gas detection to be installed with optimum monitoring placement.

Fixed flame detectors use optical sensors to detect ultraviolet (UV) and infrared (IR) radiation emitted from an open flame. Fixed gas detection includes fixed point gas detectors and open path systems, as well as ultrasonic leak detectors which listen for specific frequency sounds indicating a high-pressure gas leak.

Location of gas detectors is critical. Every target gas has a specific vapor density, some heavier than air, some lighter, and some gas types will have a density similar to ambient air. As a rule of thumb, to detect gases that are heavier than air, detectors should be placed low near the surface of the ground. When gases are lighter than air, detectors should be placed at higher levels.

The first line of detection is ultrasonic gas leak detection. Ultrasonic gas leak detectors use sensors that are designed to listen for specific frequencies in the ultrasonic sound spectrum, so they can hear when a high-pressure gas begins leaking. Ultrasonic gas leak detectors can detect high pressure leaks at the speed of sound. Additional benefits include the range of coverage provided by the detectors, leak detection of any gas type, and no impact from wind direction. Ultrasonic gas leak detectors are only suitable for leak detection in applications that have gas stored at high pressure. The detectors cannot distinguish what type of gas is leaking or where the leak is occurring in the coverage area. 

 In applications where it is important to distinguish one gas from another and to know the concentration of the target gas and the location of the leak, fixed point gas detectors can be placed where leaks are likely to occur. Sensors may use catalytic bead, infrared, or electrochemical detection methods to detect various combustible or toxic gases. In the unfortunate event that a combustible gas release reaches an ignition source, flame detectors alert the end user of the severity and approximate location of the fire so that measures may be taken to rapidly place the facility in a safe state.

Two types of monitoring patterns are generally used to determine the placement of flame and gas detectors. With source monitoring, detectors are placed close to potential sources of leaks and depending on the known possible leak sources, more or fewer detectors may be placed. This type of placement is good for medium or large releases of gas and releases of toxic gases that may move away from the area. The drawbacks of this type of placement is that there are many potential sources of leaked gas and many detectors may be required.

Volumetric monitoring uses a grid to place detectors in equally spaced locations in order to pinpoint sources and estimate volume of escaping gases. The drawbacks to this type of placement include the potential of greater gas released before detection and blockage of detection by other equipment before detection can occur.

These fundamentals give a guideline for questions that provide the basis for safety in your facility. Do you have further questions on the topics covered? Begin your search for answers here.