Safety in Hydrogen Applications - Vol 5 of 7, Flame detection technologies

Hydrogen flames emit low IR radiation which is not sufficient to trigger a thermal heat detector alarm. While thermal heat detectors are beneficial, their correct placement is the most significant challenge. An alternative solution is to use an optical flame detector capable of detecting a hydrogen flame. Unlike hydrocarbon flames, hydrogen flames emit minimal visible light. However, technologies exist that can detect hydrogen flames, including those that sense non-visible IR and ultraviolet (UV) radiation.

UV flame detectors employ anode/cathode Geiger-Mueller-type vacuum tubes, a technology that dates back to the early 20th century, to sense UV radiation emitted by a flame. UV radiation enters the vacuum tube through a quartz window and hits the cathode. The energy from the UV photon releases a photo electron, creating an electrical impulse as it travels to the anode.

As hydrogen flames primarily radiate energy in the UV band, UV flame detectors are excellent at quickly detecting hydrogen flames. However, UV flame detectors are sensitive to arcs, sparks, welding, lightning, and other UV-rich non-flame sources. These UV emitters can trigger false alarms in UV flame detectors, which can lead to costly consequences and desensitize people to real potential dangers.

Therefore, UV flame detectors are best suited for locations isolated from sources of false alarms, such as enclosed rooms. Even in these settings, the problem may not be completely eliminated, as most enclosed rooms have ventilation ducts that can reflect UV from lightning and welding, potentially causing a UV flame detector to alarm.

Detectors that utilize both ultraviolet and infrared (UV/IR) technologies exist. These detectors require both UV and IR signals to be present to trigger an alarm. This provides better false alarm rejection capability compared to just UV detection alone. However, UV/IR detectors are still vulnerable to combinations of false alarm sources.

Multi spectrum infrared (MIR) flame detection has emerged as the preferred choice for detecting hydrogen flames in most indoor and outdoor settings due to the false alarm challenges faced by UV and UV/IR flame detectors. These flame detectors use a combination of IR sensor filters and software algorithm to both detect flames and reduce false alarms.

Some MIR flame detectors have been specifically designed to detect the low-level radiation from hydrogen flames using a unique set of IR filters. These specialized devices offer a very good detection range; with the optimal IR filter set, some MIR flame detectors can detect hydrogen fires at approximately double the range of a UV flame detector. MIR flame detectors also offer a good response time and do not trigger false alarms when exposed to arcs, sparks, welding, and lightning. Additionally, they provide solar resistance and are insensitive to artificial lights and most blackbody radiation, factors that may negatively affect other detection technologies.

On the downside, the range of MIR flame detectors is reduced by the presence of water or ice on the lens. To address this issue, some detectors are equipped with lens heaters that melt ice and accelerate the evaporation of water.

The Det-Tronics X3302 is certified as SIL2. It offers maximum false alarm rejection and an extended detection range. The device is optically calibrated automatically and has built-in FDT/DTM and HART capability. It sets the new standard with a detection distance of 100 feet (30.5m) for a 75 cm/10 SLPM hydrogen plume, offering the lowest cost of coverage. It has the ability to detect smaller fires earlier, ensuring low maintenance costs and reliable fault diagnostics. The device is explosion/ flame proof (Ex d) or suitable for increased safety installations (Ex d e) in hazardous locations.

The X3302 is insensitive to artificial lighting and lightning, and resistant to solar and blackbody radiation. It offers multiple output configurations such as Relay, Relay/0-20mA, Relay/0-20mA/HART, Modbus RS485, and Eagle Quantum Premier LON/ SLC. The Automatic Optical Integrity (oi) feature provides a warning when detection is impeded.

The device comes with housing options of copper free aluminum or stainless steel. It features microprocessor-controlled heated optics and built-in data logging.