Detection of Hydrogen Released in a Full-scale Residential Garage Thomas Cleary & Erik Johnsson Fire Research Division Engineering Laboratory National Institute of Standards and Technology Gaithersburg, MD ICHS 2011 September 12-14, 2011 San Francisco, California-USA

Objective To assess whether or not a low-level leak of hydrogen gas can be detected in a residential garage space and if detectable, whether or not hydrogen concentration is uniform across the selected sensor placement locations (ceiling and wall).

NIST Indoor Air Quality House Garage Volume ~ 93 m 3 Ceiling 2.44 m high

Experimental A non-combustible gas mixture of nominally 5% hydrogen and 95 % nitrogen was released in a residential garage (forming gas) Gas mixture was released through a dispersion box located on the garage floor at a rate of 350 L/min (standard conditions) for about ¾ hour Hydrogen sensors mounted on ceiling locations and a wall location recorded concentrations during and after the gas release Tests were conducted with and without a car over the dispersion box

Idealized Case Assuming injected gas displaces garage air, then injecting 3 cylinders of forming gas would yield a well mixed hydrogen concentration of 0.8%, and the oxygen concentration would be reduced from 21% to 17%.

Dispersion Box Dispersion Box was a 30 cm by 30 cm sand burner Centrally located on garage floor Average gas exit velocity was 6.5 cm/s Low momentum plume

Sensors Catalytic bead type hydrogen sensors –range 0 % to 2.5 % –typical 90 % response time (T-90) of 2 s –relative uncertainty ± 3 % of reading (two standard deviations) –Reliable output in reduced oxygen environment (20% reduction possible due to nitrogen flow) MOS sensors experienced calibration shift

Sensor Locations

No Car Over Dispersion Box (Test 4) Initial Response CCeil – 19 s WCeil – 29 s SCeil – 40 s EWall – 49s

Car Over Dispersion Box (Test 2) Initial Response CCeil – 57 s SCeil – 70 s EWall – 84 s

Car Over Dispersion Box (Test 3) Initial Response CCeil – 58 s EWall – 80 s SCeil – 85 s WCeil – 90 s

Central Ceiling Location

South Ceiling Location

West Ceiling Location

East Wall Location

Time to Reach 0.4% Hydrogen

Ceiling Air Speed

Hydrogen Concentration Decay Experiment 2 Average air exchange rate = 0.37/hr

Conclusions The low level hydrogen leak was easily detected in the unventilated garage space A car placed over the dispersion box: –reduced peak concentration by 25% compared to the no-car case –took considerably more time to reach a threshold of 0.4 % hydrogen compared to the no-car case No clear advantage locating sensor in any of the investigated locations