This project will lead to the creation of a prototype domestic hydrogen detection device, similar in style and size to existing, ceiling mounted, indoor smoke and CO detectors. The battery powered device will include a piezo speaker for audio alarm and an LED for visual alarm and to indicate proper functioning. The device will use an available MOS sensor combined with temperature and relative humidity sensor to determine the H2 volume in air.
Over the next few years, it is intended that the current natural gas energy system will transition into a system that is fuelled by a large proportion of hydrogen gas. Hydrogen has many similar characteristics to that of natural gas but does not behave in the same way. To address these different characteristics and to increase customer confidence in hydrogen being used in domestic properties, a method of reliably detecting hydrogen leaks within the home is required.
At project completion, a pre-production prototype domestic hydrogen detection device will have been created and will have been tested in a representative environment. This device will be ready for manufacturers to use as the basis for commercially available sensors.
Objectives
The objective of the project is:
- To develop a pre-production prototype domestic hydrogen detection device that has been tested and for the device to be ready for manufacturers to use as the basis for commercially available detectors.
Learnings
Outcomes
The overall delivery of the project has been successful as DefProc completed all milestones in stage 1 and 2 and met their final project objective of delivering 10 prototype devices to HSL. Due to the delays caused by necessary firmware changes and device reviews, this meant DefProc was 8 weeks overdue on completing the final milestone. Including the timing requirements for third-party testing, the final delivery date for the project is the 31st March 2022.
The project delivered the aforementioned 10 prototype devices and associated reports from DefProc and HSE.
Currently, there is no British Standard to which a domestic H2 gas alarm must conform, but the most relevant is BS EN 50194-1:2009 Electrical apparatus for the detection of combustible gases in domestic premises. This details a number of tests, of which three were selected for testing of the prototype devices.
Findings
Testing was based on BS EN 50194-1 Electrical apparatus for the detection of combustible gases in domestic premises - Part 1: Test methods and performance requirements. This standard is not directly relevant as it makes no mention of H2 but details tests that can easily be adjusted for H2.
Tests in accordance with this standard proved too demanding for the prototypes so subsequent testing was limited to help compensate for a wider range of temperature and relative humidity that affected the devices. This resulted in improved performance but still only 2 out of 10 of the devices passed for all the conditions of all the tests.
Therefore, it is concluded:
· It is likely that with further improvements the prototype devices can pass the tests for all variations of temperature and humidity.
· The improved prototype devices would still need to be subjected to a slow accumulation of H2 gas test before their use in trials of H2 in a domestic environment.
· During H2 trials these further improved devices would have to be labelled as prototype devices for testing as they have only been challenged with some of the tests in from the Standard for flammable gas alarms.
Next Steps
Following the results of this project, further testing of the characterisation of sensors needs to be undertaken in a range of different Hydrogen concentrations and a range of temperature (15-25°C) and humidity (30-70% RH). This is to allow for the alarm tolerance to be lowered from the current ±6% LEL to ±3% LEL and meet the predicted requirements expected for a domestic hydrogen detector - once any standard to include Hydrogen is published.
Lessons Learnt
Ways the project could have been improved were:
A revision of the power supply of the devices. The current power supply uses both USB and battery power. When switching over to battery power there is a slight leak through the 5 volt line meaning some power is lost during the process. By closing the 5 volt route from the battery, DefProc would enhance the efficiency of the switch from USB to battery power and thus maximise the power provided to the device by the batteries.
DefProc could have also gone to the HSL earlier in Stage 3 (or before) as this would have sped the project up and allowed access to span gas results earlier.
The testing criteria could have been identified at an earlier stage of the project. This would have helped ensure that the firmware was created correctly from the onset in line with the required criteria and less time would have been needed to redevelop it.
Defining the testing criteria sooner would have also given DefProc the chance to use a higher concentration or ‘span gas’ of +/-3% so they would have been able to set the upper and lower alarm levels sooner and more accurately before going to HSL for stage 3’s field testing. This would have sped up the process and enabled DefProc to gain more accurate sensor responses more quickly.
The sensor required is exclusive to a single manufacturer, meaning an identical device cannot be accessed from anywhere else. This could cause problems in the future if the supplier was unable to provide them for any such reason and manufacturers of future devices would have to redevelop alternatives.
