ISO TC 197 WG13 Meets in Italy
Karen Hall, National Hydrogen Association
 ISO TC 197 working group 13 (WG13) met on November 5 & 6 in Italy, in conjunction with the World Hydrogen Technologies Convention. WG 13 is developing an International Standard for hydrogen detection apparatus. The document had been distributed for comments, and the working group has met twice to resolve the comments received. Many comments were resolved in June, when WG13 met in Seoul, Korea. The remaining comments were addressed at this meeting in Italy.
The scope of the document has changed to indicate the document is applicable for “single and/or multiple safety operations,” which means the number of actions/alarms that the detection apparatus is capable of producing can be one or more. The apparatus still must always continuously, in time domain and concentration domain, monitor hydrogen concentrations over the measuring range of the apparatus.
The WG13 convenor and secretary will prepare an official document of the resolution of the comments for ISO TC 197. The purpose of this article is to provide a short overview of the key progress made at this meeting.
One key area of progress has been in the agreement for cooperation between ISO TC 197 (Hydrogen Technologies) and IEC TC31 (Equipment for explosive atmospheres). It has been agreed that both technical committees will cooperate with each other “to make an effective and positive contribution to international standardization in matters of common interest.”
Based on several of the comments received, the working group discussed the distinction between requirements for the detection apparatus and requirements for the overall system design for a given installation. Since the document is meant to apply to the performance and test requirements for the detection apparatus which may then be used for stationary applications where continuous hydrogen monitoring is required, the system design for installations is outside the scope of the standard. The working group agreed that sensors tested in accordance with this standard may be appropriate for a large variety of installations, and therefore installation-specific requirements were not appropriate to this standard. To that end, the section on batteries was deleted from the draft because the method of backup power is a system design issue, not for the detection apparatus to decide.
There was also significant progress on the issues of measurement range and calibration. The US TAG and Canada had indicated interest in opening the measurement range defined by the standard to allow the broadest possible application of sensors that meet the requirements. WG13 agreed that the measuring range can be declared by the manufacturer based on user requirements, rather than requiring the range cover a minimum of 1000 ppm or lower. Hence, there is no limit for the declared measurement range, including above the lower flammability limit. For detectors that are intended to cover a range that includes 1% hydrogen in air, 1% or less hydrogen by volume shall be allowed to be a set point considering the importance of this concentration for safety operations.
After much discussion, the working group realized this decision would have an impact on many areas of the document, such as the standard test gas to be used, calibration curves, and tolerances, to name a few. In the case of detection apparatus with a wide range of detection, multiple concentrations of test gases for the calibration test and performance tests such as temperature test and so on may be required. First of all, the working group has decided that the declared measurement range will have to be proven by at least three calibration curves points: one at the lower end, one at the higher end and one in the middle of the declared range. If the apparatus uses two or more sensor principles to cover a wide measuring range, additional point(s) will be necessary. For the same reason, the working group also introduced an “order of magnitude” rule specifying the number of test gases which is determined by the concentration ratio of the highest detection limit divided by the lowest detection limit. If the ratio is less than ten, then use one standard test gas. If the ratio is equal to or more than ten, then use two test gases, one is the standard test gas and the other with the lower end concentration. For example, a detection apparatus that is claimed to measure hydrogen concentrations between 100 ppm and 40,000 ppm (4% vol.) will have to have at least three calibration points at 100 ppm (lower end), 20000 ppm (middle of the range) and 40000 ppm (higher end), and at least two test gas points at 100ppm (lower end) and 20000 ppm (middle of the range). Necessity of additional test points between 100ppm and 20000ppm or 20000ppm and 40000ppm are to be considered. The working group will therefore continue to work on the document to address these issues.
There was also progress in understanding the requirements in existing IEC TC 31 documents, and ensuring that CD 26142 does not conflict with existing standards, unless there is technical justification to do so. This is the case for detectors designed to measure in the range below 1% hydrogen by volume. It may also be the case for detectors that may be designed to monitor hydrogen concentrations above 4% hydrogen by volume.
Another area where it may be justifiable to deviate from published IEC standards is for the tolerance allowed in testing. For the range that is already covered by IEC, the tolerance should be the same or we need to justify why it is different. One reason could be that tolerances will be higher due to the larger range of the detection apparatus.
The following is a schedule for the follow-on actions for WG13:
- Homework list and minutes are to be distributed to WG13 members by November 19, 2007.
- Homework is due by January 15, 2008.
- Incorporate homework into the draft by January 31, 2008.
- Complete a review by convenor by February 14, 2008.
- Circulate revised draft to WG members by February 15, 2008.
- Feedback/comments on the draft due by February 29, 2008.
- Review of comments and final review by convenor and final adjustment in March.
- Target date for submission of DIS end of March.
- 5 month voting period, to include IEC TC 31.
The next meeting is likely to be held in Europe, in an effort to facilitate IEC TC 31 participation. This meeting is likely to be held in the Fall 2008 timeframe to resolve comments from the Draft International Standard (DIS).
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