What size PSA plant does a 100-bed hospital need?

Where the 90 m³/h comes from

In its interim guidance Oxygen sources and distribution for COVID-19 treatment centres (4 April 2020), which states that it expires two years after publication, WHO worked through a hypothetical 100-bed COVID-19 treatment facility: 75 severe patients at 10 L/min and 25 critical patients at 30 L/min, giving 45 m³/h for each group and 90 m³/h in total. WHO noted that the example was based on a patient count, that typical quantification would be based on the equipment available, that the flows for critical patients were only the oxygen portion of the gas, and that needs should be reassessed once the equipment is commissioned. See how to estimate hospital oxygen demand.

How WHO sizes a hospital

WHO's Foundations of medical oxygen systems (2023) lists the three most used methods to calculate estimated need:

• Beds per type of ward. WHO notes that the average hypoxaemia and flow rates used come from clinical guidelines and may not represent real practice in the facility.
• Gas wall outlets per bed in each type of ward, which is limited to facilities with a pipeline network; counting 100% of the outlets in use at maximum flow can easily oversize the source.
• Historical consumption, such as additional cylinders used per day by size, which suits facilities without piped distribution but can be unrealistic.

The calculation then applies usage factors: annual inpatient admissions, bed occupancy, the hypoxaemia rate per type of ward and the average flow per ward. WHO suggests using no more than two usage factors together to avoid undersizing, while using none of them could oversize the system. UNDP's 2025 requirements assess projected demand from inpatient admissions, bed counts, terminal outlets per bed, occupancy rates, historical consumption, average flow rates, hypoxaemia rates and future expansion plans.

Adjustments before choosing a plant

• Unmet need. Open Critical Care warns that current consumption may grossly underestimate optimal consumption, because patients who lack access to oxygen today must also be counted, and Global Fund guidance (2024) says need should not be estimated by current demand.
• Estimating errors. Open Critical Care lists leaks in the oxygen infrastructure, inaccurate estimates of device consumption and ignoring future changes in need among the common pitfalls.
• The plant's own use. HTM 02-01 (2026), the NHS England guidance, says PSA regeneration uses a proportion of the product gas, which should be taken into account when sizing the plant.
• Purity. A Global Fund briefing note (3 April 2024) gives the example of equipment producing 20 Nm³/h at 93% (±3%) that would produce 18 Nm³/h set to 95% (±1%).
• Cylinder filling. If the plant also fills cylinders, Assist International (Open Critical Care) says it should be designed for the pipeline demand plus the oxygen needed to fill cylinders, at the same time.
• Working margin. Assist International also says it is reasonable to assume 80 to 90% of the rated capacity as the plant's actual working capacity.
• Redundancy. WHO (2023) describes configurations that combine more than one plant, such as duplex or multiplex plants; see what backup a hospital should keep.

With ULTRAOX plants

To size an ULTRAOX plant, Ultra Controlo needs the oxygen flow required in m³/h or, for cylinder filling, the size and number of cylinders to fill per day. ULTRAOX ST models range from 0.32 to 164 m³/h per unit, and the plants are modular and can be expanded without replacing the concentrator. See what capacities ULTRAOX plants cover.