What should an oxygen cylinder filling station tender specify?

Section 1.2 of WHO's Technical specifications for health facility based medical oxygen systems (31 December 2024) covers a booster compressor and a filling manifold, also called a filling ramp, that compress medical oxygen from 5 to 8 bar into high-pressure cylinders, typically to about 150 bar. WHO says the generic specifications should be adapted to the project before being considered binding, and that national or regional standards take precedence over the international standards it lists.

Booster compressor

• Fill pressure: up to 150 bar, up to 200 bar or another pressure the buyer specifies, with a factory set automatic shut-off at 150 bar or another value chosen for the context.
• Type: reciprocating, oil-free on the oxygen side, air or water cooled; WHO suggests considering water cooling for warmer climates and throughput above about 15 m³/h.
• Capacity: set by the buyer, considering only the plant capacity dedicated to cylinder filling; the vendor states the compressor efficiency (inlet versus outlet flow), the suction pressure range and the compatibility with the plant.
• Safety: relief valves at each stage, automatic shut-off at the pre-set fill pressure and when 204 °C is exceeded. A shut-off on any stage temperature reference point is listed as optional and recommended, and a visual alarm for abnormal temperature rise as recommended.

Filling manifold and purge vacuum

• A cylinder rack with chains so that cylinders stay in place during purge and fill, and flexible hoses or metallic pigtails intended for high-pressure oxygen filling.
• A check valve at each cylinder connection point, listed as a recommended safety feature.
• Connections that match the cylinders: WHO lists bull-nose types (5/8 inch BSP (F)/BS 341 No. 3, CGA 540, DIN 9, NF 'F' and NEN Ri2) and pin-index (ISO 407/BS 850/CGA 870).
• A purge/vacuum pump of at least 40 m³/h reaching 0.5 mbar, and oxygen-compatible piping from booster to manifold header to ISO 15001 or equivalent.
• The number of connections, chosen for the fill interval and shift staffing; a capacity in cylinders per day must state the cylinder size and fill pressure (see how many cylinders a filling station needs).

Training, warranty and documents

The WHO table asks for on-site training for installation, testing and commissioning and for users, a warranty of at least 1 year from commissioning with remote support 24 hours a day for manufacturer defects, a preventive maintenance schedule by operating hours, a spares list for the first 10,000 hours, spare parts available for at least 10 years and a lifespan of at least 10 years guaranteed by the manufacturer. The table also asks for the station to be cleaned for oxygen service (hydrocarbons not above 220 mg/m² and no particles above 100 microns) and to carry "no oil" and "no sources of ignition" signage. In the absence of requirements from the national regulatory authority, WHO suggests alternatives such as the EU Low Voltage Directive (2014/35/EU); the standards it lists include ISO 7396-1 for piping, hoses and connections and IEC 60204 for the booster.

Acceptance tests

The Global Fund's PSA plant commissioning guidelines (28 August 2024) check that the cylinder filling rate is within 10% of the manufacturer's stated output rate, that the booster shuts off automatically at its set shutoff pressure, and that the pressures at all stages, including the inlet, meet the manufacturer's specifications. They also confirm purity with a handheld analyser directly from a recently filled cylinder.