Oxygen and PSA
Why is oxygen pressure low on the ward?
Why is oxygen pressure low at the ward outlets when the plant is running, and what can be done?
Short answer
Low oxygen pressure at ward outlets has several possible causes: WHO (2023) explains that source pressure drops along the pipeline with pipe section, network length and number of branches, and a USAID guide for Indian hospitals lists, for low oxygen tank pressure, dirty pre-filters, valves not fully open, leaks, a gauge needing calibration and consumption above production.
Assist International, answering this question on Open Critical Care, says there could be many reasons and that, where the plant feeds a pipe network, the pipe design may not have been done correctly. WHO's Foundations of medical oxygen systems (2023) explains that the pressure provided by the source drops along the distribution system depending on factors such as the section of the tube, the length of the network and the number of branches to wall outlets, and that the design must guarantee a minimum pressure at every wall outlet, from the one closest to the source to the farthest. It lists the distance from the plant to the pipeline among the location factors, to prevent pressure drop at the wall outlets, and describes dual-line regulators that hold the pressure at the value defined in the design.
What to check
| Where | Check | Source |
|---|---|---|
| Plant output | Output pressure within range: WHO's interim PSA specifications (2020, superseded by WHO's technical specifications of 31 December 2024) asked for a continuous 300 to 600 kPa (3 to 6 bar), a gauge or sensor between the source and the line pressure control, and an alarm below 3 bar | WHO, 2020 |
| Compressor intake and filters | No obstruction to the air flow near the compressor; pre-filters clean or changed | USAID RISE troubleshooting (low oxygen tank pressure) |
| Valves | All valves fully open | USAID RISE troubleshooting (low oxygen tank pressure) |
| Demand | Consumption compared with production; drawing more than the rated flow drops both purity and pressure | USAID RISE procedure |
| Instruments | The oxygen tank pressure gauge or transmitter may need calibration | USAID RISE troubleshooting (low oxygen tank pressure) |
| Leaks | Leak test of the plant, and checks for leakages along the pipeline from the source to the wards | USAID RISE troubleshooting (low oxygen tank pressure); WHO, 2023 |
| Pipeline | Pipe size matches the design drawings, or a reason for the change is documented | Global Fund commissioning guidelines, 2024 |
The USAID procedure's leak test leaves the plant isolated and pressurised, for example at 5 bar, for one hour and compares the gauge readings; any pressure drop is then traced with soapy water on joints, fittings, valves and regulators. Global Fund commissioning guidelines (28 August 2024) also ask for leak tests across the whole infrastructure, from the compressor to the bedside outlet.
When demand has outgrown the plant
Global Fund sustainability guidance (22 August 2024) asks for oxygen production to be compared with consumption every year and, if the plant is overused, suggests considering additional secondary or tertiary sources. AIGA 113/20, adopted from EIGA Doc 195, warns that when demand exceeds the nominal capacity of an oxygen 93 source, the concentration at its outlet risks falling below the 90% set point.
WHO (2023) also lists ways to use the oxygen available more efficiently: monitor and register consumption, disconnect ventilators from the oxygen source when not in use, use bedside concentrators where possible for patients who need less than 10 L/min, and check for leakages from the source to the wards.
ULTRAOX SC and ULTRAOX ST plants deliver oxygen at 6 bar in every model of their datasheet tables. The ULTRAOX 2022 datasheet says the plant starts and stops oxygen production automatically in response to demand from the downstream distribution system and is designed to keep a continuous, stable pressure in the oxygen network. For the alarms and the backup supply, see what happens when oxygen pipeline pressure drops.
More questions
What pressure should the ward outlets have?
It depends on the standard applied; as an example, WHO (2023), citing the 2021 edition of NFPA 99, reports a recommended working pressure of 345 to 380 kPa at the wall outlets.
Will an alarm warn of low pressure?
WHO (2023) describes alarm sensors and displays along the pipeline that detect a pressure drop or rise, and WHO's 2020 PSA specifications asked for an alarm when the plant output falls below 3 bar.
Sources
- Open Critical Care FAQ (Assist International): The pressure of oxygen in the oxygen plant is low in our hospital, what could be the probable reason?
- WHO, Foundations of medical oxygen systems (17 February 2023), sections 2.2.4, 2.9 and 3.3
- WHO, Technical specifications for PSA oxygen plants, interim guidance (8 June 2020)
- USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management, troubleshooting and Annexure A
- Global Fund / Build Health International, Overview: PSA Oxygen Plant Commissioning Guidelines (28 August 2024)
- Global Fund / Build Health International, Overview: Sustainability Guidance for PSA Oxygen Plants (22 August 2024)
- AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, section 4.4.1
- ULTRAOX SC datasheet, p. 5 (model table)
- ULTRAOX ST datasheet, p. 5 (model table)
- ULTRAOX datasheet 2022, p. 6
- WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.