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Liquid Hydrogen Tank Incident Leads to Second Incident

Severity
Incident
Was Hydrogen Released?
Yes
Was There Ignition?
Yes
Incident Attributes
Describe the incident, including corrective steps taken and their result.

Incident Synopsis
While attempting to replace a rupture disk in a liquid H2 vessel, H2 gas was released and ignited. In fighting the fire, liquid N2 was sprayed onto a second liquid H2 vessel located nearby. This resulted in cracking of the outer mild steel vacuum jacket. The loss of the vacuum caused a rapid increase in pressure and rupture of the burst disk of the second vessel. H2 boiled off and was burned in the fire.

Cause
The rupture disk was being replaced with a load of liquid H2 in the vessel and no separating inerting gas. The H2-air mixture was probably ignited by static discharges. Rupture of the second vessel burst disk was caused by the low-temperature exposure of the mild steel vacuum jacket.

Lessons Learned

The use of inerting gas or other means of separation should be employed when conducting mechanical work where hydrogen gas could be present. More importantly, per CGA S1.3, the vessel should be equipped with a dual relief system that can isolate one side from the other and allow a rupture disc to be changed without exposing the operator to hydrogen.

In the second incident, the cracking of the outer mild steel vacuum jacket was more than likely related to the coefficient of thermal expansion of steel, which defines how much the material will contract when its temperature is decreased. The temperature of cryogenic liquid nitrogen is at -195.8 °C (-320.44 °F), and the linear coefficient of thermal expansion of 1020 steel at room temperature is 12 x10-6 1/0 °C. Thus, the significant contraction in the steel due to the instantaneous temperature reduction created localized stresses, which cracked under the vacuum pressure of the system. Some other method of controlling the fire should have been employed. In addition, the metal would have been made much more brittle due to the low temperature.

All relevant personnel should receive at least basic training on the proper selection of fire extinguishing techniques for the given scenarios they are likely to encounter.

Liquid nitrogen should not be used to put out a hydrogen fire. It is very difficult to put out a gaseous hydrogen fire, plus had the liquid nitrogen not cracked the nearby vessel's shell, it certainly could have cracked the original vessel. It could also have plugged up the stack by freezing at liquid hydrogen temperatures.

Key:

  • = No Ignition
  • = Explosion
  • = Fire
Hydrogen Incident Summaries by Equipment and Primary Cause/Issue
Equipment / CauseEquipment Design or SelectionComponent FailureOperational ErrorInstallation or MaintenanceInadequate Gas or Flame DetectionEmergency Shutdown ResponseOther or Unknown
Hydrogen Gas Metal Cylinder or Regulator 3/31/2012
4/30/1995
2/6/2013
4/26/201012/31/1969  3/17/1999
11/1/2001
12/23/2003
Piping/Valves4/4/2002
2/2/2008
5/11/1999
4/20/1987
11/4/1997
12/31/1969
8/19/1986
7/27/1991
12/19/2004
2/6/2008
10/3/2008
4/5/2006
5/1/2007
9/19/2007
10/31/1980
2/7/20091/24/1999
2/24/2006
6/8/1998
12/31/1969
2/7/2009
9/1/1992
10/31/1980
10/3/2008 
Tubing/Fittings/Hose 9/23/1999
8/2/2004
8/6/2008
9/19/2007
1/1/19829/30/2004
10/7/2005
 10/7/2005 
Compressor 10/5/2009
6/10/2007
8/21/2008
1/15/2019
  10/5/20098/21/2008 
Liquid Hydrogen Tank or Delivery Truck4/27/198912/19/2004
1/19/2009
8/6/200412/31/1969 1/1/197412/17/2004
Pressure Relief Device7/25/2013
5/4/2012
1/15/2002
1/08/2007
12/31/1969    
Instrument1/15/20193/17/1999
12/31/1969
2/6/2013
  11/13/73  
Hydrogen Generation Equipment7/27/1999  10/23/2001   
Vehicle or Lift Truck 7/21/2011    2/8/2011
12/9/2010
Fuel Dispenser 8/2/2004
5/1/2007
6/11/2007
9/19/2007
 2/24/2006
1/22/2009
   
Fuel Cell Stack      5/3/2004
12/9/2010
2/8/2011
Hydrogen Cooled Generator   12/31/1969
2/7/2009
   
Other (floor drain, lab
anaerobic chamber,
heated glassware,
test chamber,
gaseous hydrogen
composite cylinder,
delivery truck)
 11/14/1994
7/21/2011
7/27/1999
6/28/2010
8/21/2008
12/31/1969
3/22/2018
  6/10/2019
  • = No Ignition
  • = Explosion
  • = Fire
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