What site design conditions should a PSA tender specify?

Climate and altitude

The WHO Technical specifications for health facility based medical oxygen systems (31 December 2024), which supersede WHO's 2020 interim PSA specification for oxygen generator plants, ask for continuous operation within specification at an ambient temperature of at least 5 to 40 °C, concurrent with relative humidity of 15 to 95%, and leave the elevation for the buyer to specify in metres or feet above sea level. A footnote says every 300 m of variance in elevation could affect the performance and efficiency of the unit. Where the operating environment is outside this range, the vendor is to propose measures to protect the equipment and keep it running.

The same table links two components to the site: the air compressor is to be sized for the generator's output (a minimum of 5 times the expected output plus the accommodation required for elevation), and the supplier is to justify the dryer type and size against the local conditions, since a refrigerant dryer's size depends on ambient temperature and humidity and a desiccant dryer is to be considered for colder environments or at elevation. The 2020 interim specification had asked for 10 to 40 °C, 15 to 95% relative humidity, preferably simultaneously, and 0 to 1,000 m as a minimum; UNDP's REQ-OXY-001 still refers its minimum specifications to that 2020 document.

Site data the buyer collects

In UNDP procurement, REQ-OXY-001 (effective 1 January 2025) says site-specific factors such as elevation, temperature, humidity and dust should be considered during design, and asks for the plant to be housed in a structure that protects it from precipitation, wind and dust. Its site evaluation form (Annex II), to be completed two weeks before the equipment arrives, records, among other items:

• the highest monthly average temperature, the altitude in metres above sea level and the highest monthly average humidity;
• whether the housing is in a floodable or seismic area;
• the distance from the air intake to the nearest contaminant source, and whether the intake is protected from insects and precipitation;
• the ventilation of the housing, natural or forced, considering temperature and humidity.

UNDP's sample commissioning report (Annex III) then checks that the plant room temperature is kept between 5 and 40 °C, with a device monitoring temperature and humidity. More on each factor: altitude, heat, humidity and dust and sand.

Power supply

See what power supply a PSA plant needs.

ULTRAOX plants

The ULTRAOX datasheet (2022, p. 9) asks for ambient air reasonably free from dust, at an acceptable level of humidity and free from chemical contamination, for a location whose electrical designation is not hazardous, and for the customer to provide three-phase power and condensate drainage.