Hydrogen cylinders and storage tanks should be stored outside at a safe distance from structures, ventilation intakes, and vehicle routes. This applies even while in use. Best practices call for compressed hydrogen bottles supplying a manifold to be located outside, with welded lines to connect to indoor equipment.
If a hydrogen cylinder is used inside, additional safety considerations must be addressed, including (but not limited to):
- limiting total hydrogen volume based on workspace size
- maintaining minimum spacing between cylinders of hydrogen and oxidants
- securing of cylinders properly
Additional recommendations for cylinder storage inside a shed or other enclosure include:
- Buildings (e.g., sheds) used for storing hydrogen cylinders should be constructed of noncombustible materials.
- Detached storage facilities should have normal and emergency ventilation system with inlets low to the ground and exhausts at the highest point of the room in the exterior wall or roof. The inlets and exhausts should be oriented in the same direction (for wind tolerance).
- Hydrogen sensors should be installed at the exhaust within the enclosure to detect any leaks.
- The storage facility should have an automatic shutoff that activates if a leak is detected or a problem occurs in the facility that is being supplied with hydrogen.
- Ignition sources (e.g., open flames, electrical equipment, or heating equipment) should not be allowed within the storage facility.
- The gaseous hydrogen system should be electrically bonded and grounded.
Hydrogen storage facilities should be equipped with venting systems for both normal operating requirements and emergency situations. Vent lines for hydrogen (including pressure relief lines and boil-off from cryogenic systems) should be vented to a safe outside location. The vent should be designed to prevent moisture or ice from accumulating in the line. Unused hydrogen should be disposed of by venting or possibly flaring.
The vent system should:
- be leak tight
- avoid air intrusion or be designed to handle the possibility of an explosion inside the piping
- be unobstructed and protected from the weather
- safely release the unused hydrogen above the facility roof or at a remote location
- be designed to carry the excess flow of the venting gas or liquid
According to NASA guidelines, for hydrogen vent rates greater than 0.5 lb/sec, flaring may be considered. Large quantities of unused hydrogen that can't be handled by the vent system should be flared at a remote location. It should be assumed that hydrogen in vent systems will ignite, so the systems should be designed to maintain their integrity and not present hazards to their surroundings. This is not an issue for smaller commercial systems.
Flare systems must have:
- pilot ignition
- flameout warning systems
- a means to purge the vent line