Safety in Hydrogen Applications - An article series. Vol 2 of 7

ROLE OF SAFETY SYSTEM

Ensuring personnel safety and maintaining the integrity of the process system is a common requirement across all hydrogen applications. Hydrogen gas, which is highly flammable, colorless, odorless, and typically undetectable by human senses, necessitates the use of combustible gas detectors. These detectors should be installed in all areas where hydrogen leaks, spills, or hazardous accumulations could potentially occur.

The hydrogen detection system needs to be compatible with other systems, such as fire detection and fire suppression systems. Detectors must be certified for performance and safety to ensure they do not serve as an ignition source. The total time for detection, data summary, transmission, and display should be minimized. Furthermore, hydrogen gas detectors must be strategically placed and regularly maintained.

In certain applications, continuous automatic sampling equipment may be required, with sample points strategically located. This equipment should be calibrated to provide a repeatable response. The detection of liquefied hydrogen cannot rely solely on observation. While a cloud of frozen air and moisture may be visible, it is not a reliable indicator of a hydrogen leak, as similar clouds of water vapor may also rise from cold, exposed surfaces in the absence of a hydrogen leak.

The number and distribution of detection points, as well as the time required to shut off the hydrogen source, should be determined within a safety case and based on factors such as potential leak rates, ventilation rates, and the volume of space in an interior location. The detection signal should also trigger warning alarms and automatically initiate shutoff where required.

For enclosed areas where a buildup of hydrogen is possible, detection and alarm at 1 percent by volume hydrogen concentrations in air, equivalent to 25 percent of the LFL, is required (29 CFR 1910.106 1996). For permit-required confined spaces, detection and alarm at 0.4 percent by volume hydrogen concentrations in air (equivalent to 10 percent of the LFL) is required (29 CFR 1910.146 1996, and 29 CFR 1910.106 1996).

Under conditions where the sensor cannot be located at a leak source, it may be necessary to conduct a gas sample through a sensing line to the sensor. The response time under such conditions depends on thelength of the sensing line.