# How loud is a PSA plant, and why does it vent at each cycle?

**How loud is a PSA oxygen plant, why does it vent air at each cycle, and where can it be placed near wards?**

WHO's technical specifications (December 2024) set a maximum noise of 80 dBA for an oxygen generator plant's feed compressor and ask for a silenced nitrogen outlet; the plant vents at each cycle because, PATH (2023) explains, the control valves release the pressure and the nitrogen-rich air from the saturated adsorption vessel.

## Why it vents

PATH's November 2023 report on PSA plants describes the cycle: control valves direct clean compressed air into one of two adsorption vessels, the zeolite adsorbs nitrogen under pressure, and once it is saturated and the oxygen collected, the control valves release the pressure and, with it, the remaining nitrogen-rich air, before the process repeats with the other vessel. The USAID RISE operating procedure (March 2022), written for hospitals in India, adds that, during the desorption phase, solenoid valves let the nitrogen from the two towers be exhausted.

AIGA 113/20, adopted from EIGA Doc 195, says this produces a significant volume of waste gas, oxygen-depleted or oxygen-enriched air, likely to create oxygen-deficient or oxygen-enriched atmospheres around the vents, and that dust from the adsorber beds, an irritant, can also be present in the vent gas. It asks for all vents to be directed to a safe location outside buildings, away from personnel and equipment, never into an air conditioner inlet, and for consideration to be given to reducing the noise to an acceptable level according to local legislation.

## Where the noise comes from

- Sources: AIGA 113/20 says the noise of the oxygen 93 supply system, including the air and oxygen compressors, the adsorber vessels, vents and pressure relief valves, shall be considered for the potential hazard or nuisance to employees, patients and neighbouring areas, with noise abatement and ear protection in accordance with national and local regulations.
- Compressor: WHO (2024) sets a maximum of 80 dBA for the air feed compressor of an oxygen generator plant, with additional soundproofing if more power is required, and lists ear defenders in the protective equipment for operators.
- Nitrogen outlet: WHO (2024) asks for the nitrogen by-product outlet to be silenced, with a duct hose for the nitrogen exhaust. In its section on plantroom noise, NHS England's HTM 02-01 (2026) notes that exhausts from electronic drains and purge valves may also require silencing, because the pitch and volume of the noise may cause a nuisance.
- Faults: PATH (2023) names leaky valves among the common faults of the plants in disrepair it reviewed, with low purity output, fire and/or noise as results. The USAID procedure asks operators to watch at start-up for abnormal sounds in the towers and the exhaust blowdown, and to check the silencer for clogging every year; see [signs of a failing switching valve](https://library.ultracontrolo.com/answers/what-are-the-signs-of-a-failing-psa-switching-valve/).

## Placing the plant near wards

- Housing: WHO's Foundations of medical oxygen systems (2023) asks for a covered structure that, among other things, assures noise reduction during operation, and UNDP's requirements (effective 1 January 2025) ask for a structure that reduces operational noise. For containerised plants, WHO (2024) lists acoustic insulation with a minimum 10 dBA reduction.
- Exhaust: WHO (2023) asks for the nitrogen discharge duct to be vented to the atmosphere and suggests that it terminate at least 3 m clear of any door or window that can be opened, or other ventilation or air intake, with its end turned downward.
- Checks: the Global Fund commissioning guideline (28 August 2024) asks whether the plant housing ensures an acceptable noise level near the hospital wards, and its post-commissioning form (12 September 2025) whether the plant is in an area where equipment noise is not objectionable.

In ULTRAOX plants, each ULTRACON concentrator includes an exhaust gas silencer and a set of electro-pneumatic valves and regulators, and the ULTRAOX Technical Data Sheet (2022) states that ULTRAOX cycles are widely spaced, reducing the number of valve operations and moving parts over the years. For noise from medical air compressors, see [how noisy a medical air plant is](https://library.ultracontrolo.com/answers/how-noisy-is-a-medical-air-plant/).

### Is the gas vented by a PSA plant dangerous?

AIGA 113/20 says the waste gas can create oxygen-deficient or oxygen-enriched atmospheres around the vents and can carry irritant dust from the adsorber beds, and asks for all vents to be directed to a safe location outside buildings.

### How far should the nitrogen exhaust be from windows?

WHO (2023) suggests that the nitrogen exhaust terminate at least 3 m clear of any door or window that can be opened, or other ventilation or air intake.

## Sources

- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), sections 1.1, 1.1.1 and 1.3](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)
- [PATH, Pressure swing adsorption plants: Common issues and solutions to prevent future disrepair (November 2023)](https://media.path.org/documents/Root_cause_analysis_report_external_clean_v2.pdf)
- [USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management (March 2022)](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, sections 6.8 and 6.9](https://asiaiga.org/uploaded_docs/en_AIGA_113_20_Generation_of_Oxygen_93_for_Medicinal_Use.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023), sections 2.2.3 and 2.2.4](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [UNDP, REQ-OXY-001 v01, Technical and regulatory requirements for oxygen plants (effective 1 January 2025), section 6.3](https://healthimplementation.undp.org/wp-content/uploads/2025/01/REQ-OXY-001-v01-UNDP-TECHNICAL-REGULATORY-REQUIREMENTS-FOR-OXYGEN-PLANTS.pdf)
- [NHS England, HTM 02-01 Part A (2026), paragraph 17.150](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [Global Fund / Build Health International, Overview: PSA Oxygen Plant Commissioning Guidelines (28 August 2024)](https://resources.theglobalfund.org/media/qp3h1vxo/cr_c19rm-psa-oxygen-plant-commissioning_overview_en.pdf)
- [Global Fund / Build Health International, Post-Commissioning Assessment Form for Medical Oxygen Plants (12 September 2025)](https://resources.theglobalfund.org/media/pt5cp0u5/cr_c19rm-post-commissioning-assessment_form_en.pdf)
- [ULTRAOX Technical Data Sheet 2022, p. 4 and p. 14](https://www.ultracontrolo.com/products/ultraox)

Reviewed: 2026-10-23. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-loud-is-a-psa-plant-and-why-does-it-vent/