Hydrogen Vent Blow Down
Hydrogen was released near the ground when the vent line from a 13,000-gallon liquid hydrogen storage vessel suffered damage from unusually high winds. The toppled vent line did not shear or tear, but sustained a kink that restricted hydrogen flow and created a back pressure on the vessel relief system.
Repair efforts were hampered by the potential for cold hydrogen gas, a flammability hazard, in the work area. Shut off or redirection of the hydrogen was not possible, and variable breezes made set up of safe zones uncertain. A protocol had not been prepared for this scenario.
- Ventilation System
- Venting System
- Vent piping and cap
Mounting hardware incorporated polymeric braces not suitable for long-term exposure to sunlight and temperature extremes. With time, the polymeric materials had disintegrated, allowing the mounting brackets to become loose. In addition, the mounting brackets were all oriented with a degree of freedom in the same direction such that drag forces from strong wind coming from just the right direction were able to dislodge the vent line and blow it down. Periodic inspections and maintenance operations failed to pick up the deteriorating hardware.
Hardware design must be adequate for weather conditions and materials selection must be compatible with temperature excursions and solar-UV exposure conditions. Operations must include periodic inspection of mounting hardware.
Emergency procedures must address conditions that include the presence of a hydrogen leak that may pose a hazard to personnel attempting repair operations. Procedures were developed by:
- Determining the approximate temperature and release rate of the hydrogen emanating from the damaged vent,
- Finding computed hydrogen dispersion information based on diffusion and wind (see combustible cloud length as a function of release rate in Edeskuty, Frederick J. and Walter F. Stewart, Safety in the Handling of Cryogenic Fluids, Plenum Press, New York, 1996), and
- Using the dispersion information to establish a safe working area for repair operations and an exclusion zone around the hydrogen release point.