Certified Hydrogen Sensors
by Karen Hall
Vice President, Technical Operations of the
National Hydrogen Association

The main purpose of codes and standards is to ensure safety. A number of developing codes and standards require the ability to detect hydrogen concentrations before a fraction of the flammable or explosive limit is reached, in order to allow for purging, shut-off, and similar safety operations.

There are many gas and vapor detectors available commercially today. There are also efforts to develop hydrogen-specific sensors for the wide-scale commercialization of hydrogen vehicles, stationary and portable power systems, and infrastructure applications.

A question that comes up frequently at the working group level of standards development organizations is this: Are there currently hydrogen detectors that are certified to the existing standards for hydrogen detectors? If so, it would be possible to reference the existing sensor standard in developing work items. If not, what is needed to get to that point?

In the U.S., “ANSI/UL 2075 - Flammable Gas Sensors” applies. This standard covers gas and vapor detectors and sensors intended to be employed in indoor and outdoor “unclassified” locations in accordance with the national electrical code.

In Europe, “BS EN 50073 - Guide for selection, installation, use and maintenance of apparatus for the detection and measurement of combustible gases or oxygen” applies. This British Standard was approved by CENELEC in 1998.

There is a growing need for hydrogen sensors of various sizes and sensitivities for use in providing system safety. Working group members developing standards need to know what sensors are available, which standards they conform to, and whether they are certified to those standards. Companies and research organizations developing hydrogen sensors need to know what the requirements are in terms of conformance, size, and sensitivity.

In the U.K., a working group of industry and government is drafting an installation guide for hydrogen fuel cells and associated equipment that is to apply to all stationary fuel cell devices/installations fuelled by hydrogen and ventilated to the outdoors. One section of the draft installation guide reads: “The enclosure(s) containing the fuel cell and other hydrogen handling equipment and fittings should be fitted with suitable, e.g. conforming to BS EN 50073:1999, appropriately located hydrogen detectors that alarm at <10% LEL and isolate hydrogen and electrical power at <25% LEL. The isolation of the hydrogen supply should occur at a point outside the building.”

At the last meeting on 25 August, I asked if the group was aware of any sensors that meet this requirement that are suitable (size is the main issue) for this application. The manufacturers present said they are not, and that this presents a problem for them in meeting the requirement. I indicated that the U.S. has “ANSI/UL 2075 - Flammable Gas Sensors”, and that I would try to determine if there are any sensors certified to this standard, as well as to BS EN 50073. There was a general feeling that there may be sensors out there that conform to the applicable standards, but may not have been certified as such. It can be prohibitively expensive for small companies, in particular, to fund a certification program for an item that is produced currently in small quantities.

UL is going through a similar process. Draft UL 2264B defines the construction and safety requirements of hydrogen generators. In a section on detectors, the draft currently reads “Gas sensors relied upon for safety shall comply with UL 2075, Standard for Gas Sensors and be suitable for the particular vapors and gases they are intended to detect.” I have sent an email to UL asking if they are aware of hydrogen sensors that meet this requirement.

So, I put it to you, the hydrogen community. Do you have, or are you aware of any hydrogen sensors that are certified to either of these standards? Do you know of hydrogen sensors that comply with either standard but may not be certified as such? Do you feel that a funded effort to certify hydrogen sensors would fill a need in the hydrogen community? How should the developing standards be worded in advance of an adequate range of certified hydrogen sensors?

If you would like to contribute to this discussion, please email me at HallK@HydrogenAssociation.org. The next meeting of the U.K. working group will be November 10, 2004 in the NHA’s U.K. office in Gateshead, so responses prior to then will be appreciated.