6.2 Cryogenic Supplies, Reserves, EOSC, IBER & Oxygen Concentrators

Manifolds for Portable Cryogenic Liquid Containers

Portable liquid containers (dewars) on a manifold follow rules like those for gas manifolds, with additions:

• Location: outdoors in an enclosure used only for such containers, or indoors in a room used only for them. The primary and secondary headers are in the same enclosure. The reserve header may be in the same enclosure or in another compliant enclosure.
• Two equal liquid headers, each with enough vaporization capacity for the required peak flow and enough container connections for one average day's supply
• A reserve header with gas cylinder connections for one average day's supply, but not fewer than three connections. It connects downstream of the primary/secondary headers and upstream of the final line regulators.
• A pressure relief downstream of the reserve connection and upstream of the final line regulators, set 50% above the nominal inlet pressure
• Hybrid option: one liquid header (primary), one gas cylinder header (secondary) with equal capacity for peak flow, plus a reserve cylinder header
• Automatic control of primary, secondary, and reserve. Boil-off gas from the secondary header is conserved and fed upstream of the final line regulators. The reserve activates automatically if the primary and secondary cannot supply.
• Signals to all master alarms for changeover, secondary low (hybrid systems), reserve in use, and reserve low (one average day's supply)

Separation distances for portable cryogenic containers outdoors

Bulk Cryogenic Fluid Central Supply Systems

Bulk systems are covered by text extracted from NFPA 55, and the source valve marks the boundary between NFPA 55 and NFPA 99. Their automatic operation works like this:

1. While the primary supply is feeding the system, the reserve is prevented from feeding until the primary falls to the reserve activation pressure.
2. If the primary cannot supply, the reserve starts automatically.
3. With a primary vessel, a secondary, and a reserve, the cascade is primary, then secondary, then reserve. Vessels may rotate roles, for example on a timed basis, as long as that cascade is always maintained.
4. A cryogenic reserve vessel conserves boil-off gas and discharges it into the line upstream of the final line regulator assembly.

Master alarms report low contents when the main supply reaches one average day's supply, reserve in use, reserve low (one average day's supply), and reserve pressure too low for the system.

Emergency Oxygen Supply Connection (EOSC)

An EOSC lets a temporary oxygen source, such as a liquid tanker or trailer, feed the building in an emergency or during maintenance. It is required where either of these applies:

1. The bulk liquid or cryogenic fluid central supply system is outside of and remote from the building, and there is no connected in-building oxygen reserve holding one average day's supply.
2. Multiple freestanding buildings are served from a single oxygen source, so damage to the connecting line could cut off one or more of them. In that case each building gets its own EOSC.

Location:

• On the exterior of the building served, where emergency supply vehicles can reach it at all times in all weather
• Connected to the main supply line immediately downstream of the main shutoff valve

Components:

1. Physical protection against tampering
2. A female inlet sized for 100% of system demand at the emergency source pressure
3. A manual shutoff valve to isolate the EOSC when it is not in use
4. Two check valves: one downstream of the EOSC and one downstream of the main line shutoff valve, both upstream of the tee joining the two lines
5. A relief valve sized to protect downstream piping from pressures more than 50% above normal line pressure
6. Any valves needed to connect the emergency supply and isolate the normal source
7. At least 3 ft (1 m) of clearance around the EOSC
8. Four alarm connection points wired to both master alarm panels, so the temporary supply can be monitored while in use

In-Building Emergency Reserve (IBER)

• An IBER is not a substitute for the bulk system's required reserve.
• When an IBER is used in place of an EOSC or for other purposes, it goes in a room or enclosure built and ventilated to the central supply location rules.
• It consists of a gas cylinder header with at least one average day's supply, or a gas cylinder manifold. The number of connections is chosen with the delivery schedule, nearby alternate supplies, and the facility emergency plan in mind.
• A check valve in the main line on the distribution side of the normal source's main line valve keeps gas from flowing back from the reserve to the normal source.
• A local status signal, plus an alarm at all master alarms when, or just before, the reserve begins to serve the system

Oxygen Concentrator Supply Units

Arrangement: in the two-source arrangement, one source is the concentrator supply source and the second is a cylinder header with enough connections for one average day's supply. NFPA 99 also permits three-source arrangements, with additional requirements for isolation, relief valves, and line pressure controls. Category 2 systems may use the two-source arrangement with a cylinder header.