First Hydrogen Sensor Just Published
by Paul E. Patty, Sr., and John L. Parssinen

On October 18, 2004 Underwriters Laboratories Inc. (UL) announced the publication of the Standard for Safety ANSI/UL 2075 Gas and Vapor Detectors and Sensors. Products such as hydrogen detectors and sensors covered by this Standard are intended to reliably and accurately detect the presence of gases and vapors in the area in which they are installed. The gases, vapors and the extent of the areas to be protected by the individual detectors are described in the individual UL Listing, which identifies equipment that has been UL certified. Listings for this equipment, which include hydrogen gas sensors, are published in the Fire Protection Equipment Directory under the category for Gas and Vapor Detectors and Sensors (Category Code FTAM). This information is also available through the UL Online Certifications Directory located at www.ul.com.

System gas detectors and gas sensors are intended to be connected to an emergency alarm system control unit, which is used to generate a system alarm signal upon sensing an unacceptable concentration of a particular vapor or gas, such as hydrogen. The detector may operate by activating a signal at a given concentration of vapor. The sensor may transmit information defining the concentration level to the control unit, which in turn, determines when to generate a system alarm signal. Detectors and sensors that transmit concentration level information have only been investigated with compatible control units as specified in the individual Listings.

The installation wiring diagrams and instruction manuals provided by the manufacturer with these detectors are used for UL’s certification program. These documents include information describing the proper installation, operation, maintenance, and testing of the detectors.

The performance tests in ANSI/UL 2075 are used to help determine the reliable performance of the product. This portion of the certification program generally includes a series of tests as follows:

1. False signaling due to environmental conditioning tests such as: variable temperature, humidity, corrosion, accelerated aging (operation at elevated temperatures to shorten test time periods), and stability (a series of tests that exhibit the ability of a detector/sensor to function without interference from its surrounding environment);

2. Mechanical abuse tests to evaluate the stability of the mechanical assembly and circuit connections such as: jarring, vibration, and drop/impact for portable equipment; and

3. Various electrical tests for general performance such as: endurance (6000 cycles of operation on the electronics), variable input voltages, transients, abnormal operation, component temperature, and static discharge.

As part of these tests, the acceptable operation (or sensitivity) of the product is verified before and, depending upon the conditioning, either during or immediately after each test. This involves examining control equipment for minimum required operation and verification of stable sensitivity for detection products.

Additionally, these tests are conducted to determine that no false alarms occur and to confirm that conditioning tests do not have an adverse affect on the threshold response for gas and vapor detectors when adjusted to maximum sensitivity settings.

With regard to trip levels, detectors are investigated to ensure that they consistently trip at levels within 5% of the gas concentration levels indicated in the individual installation diagrams.

UL certified devices to detect ignitable air vapor mixtures such as hydrogen are capable of activating an alarm signal at 25% of the Lower Explosive Limit (LEL) for the vapors to be detected. In some cases, products will be capable of detecting even lower concentrations and will be investigated accordingly. Units designed to detect toxic vapors or vapors which present a health hazard to the user are capable of alarm activation at 50% of the Immediately Dangerous for Life and Health (IDLH) level or less, as established in the following documents:

* Permissible Exposure Limits (PEL'S) "Federal Register, Code of Federal Regulations 29. CFR, sub-part Z". Published 7-1-94 (Annually; every July)

* Threshold Limit Values (TLV'S) "Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices" Published Annually (1994-1995) by American Conference of Governmental Industrial Hygienist.

* Indoor Air Values "Ventilation for Acceptable Indoor Air Quality" "Published 1989, by American Society of Heating and Refrigeration Engineers (ASHRAE)

* Recommended Exposure Limits (REL'S) "Recommendations for Occupation and Safety Health Compendium of Policy Documents and Statements". Published 1-92, Publication No. 92-100 by National Institute of Safety Health (N.I.O.S.H.)

Equipment tested to ANSI/UL 2075 has only been investigated for use in ordinary (unclassified) locations as defined in the National Electrical Code, NFPA 70. Detectors that have additionally been investigated for use in: (1) atmospheres which might contain an ignitable mixture of flammable vapors, (2) atmospheres containing a vapor mixture which might be subject to detonation or explosive deflagration, and (3) Classified (Hazardous) Locations are included in the Hazardous Locations Equipment Directory.

To submit a gas and vapor detector or sensor, or if you have any questions regarding UL 2075 please contact one of UL’s Customer Service Professionals at 1-877-854-3577.