# Active vs passive anaesthetic gas scavenging

An active anaesthetic gas scavenging system uses a pump, fan or vacuum source to draw waste gas away under negative pressure, while a passive system relies on the patient's exhalation to push it out; the NHS England guidance HTM 02-01 (2026) recognises only fully active systems.

Both kinds remove the excess gas that leaves the anaesthetic breathing system. The difference is what moves the gas. OSHA describes a system as passive when no vacuum or negative pressure is used: the patient's passive exhalation raises the pressure in the disposal tubing above atmospheric. In an active system the disposal tubing is under negative pressure.

|  | Active scavenging | Passive scavenging |
|---|---|---|
| What moves the gas | A powered pump, fan or vacuum source | The patient's exhalation |
| Pressure in the disposal tubing | Negative | Above atmospheric |
| Typical disposal route | Fixed pipework to an extract plant kept separate from medical vacuum (HTM 02-01); OSHA also cites a central vacuum system as an example | A duct, or the exhaust grille of a non-recirculating ventilation system (OSHA) |
| Limitations noted | Needs a powered plant; HTM 02-01 asks for a duplex pump set | A separate line per operating room, wind can reverse the flow, and ice or nests can block the outlet (OSHA) |
| NHS England guidance (HTM 02-01, 2026) | The only type covered, as high-flow or low-flow systems | Not used in the UK and not recognised |

## What the standards and guidance say

ISO 7396-2:2007 covers anaesthetic gas scavenging disposal systems, with the aims of patient safety and of minimising the exposure of staff to anaesthetic gases and vapours. It requires the avoidance of cross-connections between scavenging disposal systems and medical gas or vacuum pipelines. Its terminal units are specified in ISO 9170-2:2008, which defines two types according to whether the power device is upstream or downstream of the terminal unit.

HTM 02-01 (2026) describes AGSS as low-pressure systems powered by an electric pump or fan, removing waste gas from the breathing circuit through fixed pipework, and says an AGSS should not be incorporated into vacuum systems. It notes that passive, semi-passive and hybrid systems have been used in the past, but it does not recognise or cover them.

OSHA notes that active systems are thought to be more effective than passive systems at reducing waste anaesthetic gas concentrations.

## ULTRASEG

ULTRASEG is an active system: Elmo Rietschle vacuum pumps draw anaesthetic gas mixtures at a suction level of −0.2 bar, through terminal units with an adjustable orifice that sets the flow. In the duplex version one pump runs while the other is on standby or in maintenance.

### Can the medical vacuum system be used for scavenging?

HTM 02-01 (2026) says an AGSS should not be incorporated into vacuum systems, and ISO 7396-2 requires the avoidance of cross-connections between scavenging disposal systems and medical gas or vacuum pipelines.

### Are passive systems still allowed?

That depends on the country's rules. In England, HTM 02-01 (2026) says passive systems are not used and are not recognised.

## Sources

- [OSHA, Anesthetic Gases: Guidelines for Workplace Exposures (revised 2000)](https://www.osha.gov/waste-anesthetic-gases/workplace-exposures-guidelines)
- [NHS England, HTM 02-01 Medical gas pipeline systems, Part A (2026 edition), paras 4.125, 12.2, 12.4, 12.5, 12.26 and Chapter 12 note](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)
- [ISO 7396-2:2007, Medical gas pipeline systems, Part 2: Anaesthetic gas scavenging disposal systems (iso.org summary)](https://www.iso.org/standard/41945.html)
- [ISO 9170-2:2008, Terminal units for anaesthetic gas scavenging systems (iso.org summary)](https://www.iso.org/standard/42056.html)
- [ULTRASEG datasheet, pp. 2 and 3](https://www.ultracontrolo.com/products/ultraseg)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/compare/active-vs-passive-agss/