by Carl Lawes, Blease Service Manager.

The Need

Active Gas Scavenging Systems (AGSS) were introduced to enhance the safety of the environment in which members of staff in close proximity with waste anaesthetic gases and vapors (agents) work.

A number of studies carried out both in the UK and in the U.S have shown that repeated exposure to small quantities of anaesthetic gases can adversely affect health.


The primary causes for concern from the studies is:

  • Reduced fertility levels in females
  • Increased risk of spontaneous abortion
  • Congenital abnormalities in children
  • Increased risk of cancer for females
  • Adverse effects on liver and kidneys
  • Reduced audiovisual response

For further reading: Controlling Exposures to Nitrous Oxide During Anaesthetic Administration

Waste Anaesthetic Gases and Vapors (By request)
(Tel 00 1800 3564674 <NIOSH>) 

Reproductive Hazards of Work (Author A.C Fletcher)
(Tel 0161 8339244)

Waste Anaesthetic Gases
(British Journal of Anaesthesia 82 (5): 764-6 (1999)


Controlling Exposure

There are three methods of controlling the level of exposure:

  • Ensuring adequate ventilation
    (e.g. forced air)
  • Good Work Practices
    (Covered in "Controlling Exposures to Nitrous Oxide During Anaesthetic Administration")
  • Active Gas Scavenging Systems

Active Gas Scavenging Systems

Simplistically this can be broken down into four component areas:

  • Plant (main fan)
  • Interconnecting pipework
  • Terminal outlet
  • Transfer hose & Receiving Unit

The purpose of the system from the plant to the terminal outlet is to provide the extraction flow rates to remove waste anaesthetic gases from the receiving unit reservoir. The role of the receiving unit is to provide a safe interface between the patient and the extraction flow rates.

The Standard

BS EN 740:1999

Anaesthetic workstations and their modules. Particular requirements.

Also numbered BS 5724-2.204:1999.

Replaces BS 5724 Part 2:Section 2.13:1990 and BS 6834:1987

What the change means at a glance:

Standard / Measurement


BS EN740

Extraction Flow Rate

130 - 80 L/min

75 - 50 L/min

Induced Flow

0.5 L/min

0.05 L/min


The new standard is quite involved, for a full understanding of the requirement it is suggested that the document be read fully.

The extraction flow rate ensures that waste anaesthetic gases are adequately removed from the system.

The importance of this flow rate is that if it falls too low it may not be sufficient for waste gas removal. This would lead to the waste gases spilling out from the base of the receiving unit reservoir into the immediate working environment; if too high it may lead to an increase of the induced flow at the patient connection port.

The induced flow rate should be as low as possible with the system ideally being passive between the patient and the receiving unit and active from the receiving unit to the exhaust point.

The value of the induced flow is the level of fresh gas flow that the receiving system is actively sucking out of the patient circuit. If low flows are in use the effect of a poor receiving unit on the circuit can be quite dramatic. It would appear as a leak on the system potentially causing gradual collapse of the bellows on bag in bottle ventilators as well as causing low-pressure alarms.

Transfer Hose

The transfer hose should always be fitted with a pressure relief valve (10cmH2O) such that if the transfer hose were to become occluded for any reason the patient would still have an expiratory path.

Help & Solutions

Blease Medical offers a full maintenance service to support receiving units. Providing detailed reports on our findings along with reduced service exchange rates for replacement of failing receiving units, these meet BS EN740 and are able to maintain induced flow rates below 0.05 L/min at extraction flow rates between 130 - 50 L/min.


For further information or arrange a site visit please contact Blease Service at:

Telephone: 01494 784422 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Or visit our web site at

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