GUIDANCE FOR THE SAFETY OF EMPLOYEES EXPOSED TO ANAESTHETIC
GASES
Author
Policy Ratified by
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Area Applicable
Ref No:
Committee
OSHEU
University Wide
Date Issued
Date
15/02/05
Review Date
Version No:
1
Disclaimer
When using this document please ensure that the version you are using is the
most up-to-date.
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Occupational Safety, Health and Environment Unit/Revised May 2004/Anaesthetic Gases and Vapours
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E/1
Code of Practice and Guidance for the
Safety of Employees
Exposed to Anaesthetic Gases & Vapours
Contents
Page No:
1. Introduction
2. Hazards Attributed To Anaesthetic Gases
3. Hazards Control
4. Assessment
5. Ventilation
6. Scavenging
7. Maintenance Schedule
8. Monitoring
9. Action Following Assessment
10. Staff Training
11. Pregnancy
12. References
2
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3
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Appendix 1 - Staff Advice Note
Appendix 2 - HSC Standards For Anaesthetic Gases
Appendix 3 - Example Hazard Control Sheet
Appendix 4 - Bs6834 1987 Definitions
6
8
9
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1. Introduction
Surveys were conducted in 1985 and 1998 on the occupational exposure to nitrous oxide1,2. They
concluded that exposure to anaesthetic gases was greatest for anaesthetists and that an anaesthetic
nurse's exposure could also be substantial. they recommended that theatre ventilation systems and
scavenging equipment be properly maintained and that regular monitoring of staff exposure should be
conducted. Epidemiological reports of the 1970s suggested there might be an increase in miscarriages
in anaesthetists and for this reason female members of staff contemplating pregnancy or in early
pregnancy were advised that they could opt out of work in theatres or recovery rooms3.
The Health Services Advisory Committee introduced new Occupational Exposure Standards in 1996,
under the Control of Substances Hazardous to Health regulations4,5.
2. Hazards Attributed To Anaesthetic Gases
Studies have shown that there are numerous alleged health effects associated with the exposure of
waste anaesthetic agents6,7. These include an increased risk of spontaneous abortion to females
exposed to anaesthetics; the risk is greatest in the first trimester, with incidence 1.5 - 2 times greater
than in unexposed females.
One of the recognised health effects resulting from the exposure to Nitrous Oxide is that of bone
marrow suppresion8. This study showed definite evidence of altered DNA synthesis in the bone marrow
and mild megaloblastic changes after exposure to working levels of Nitrous Oxide. These changes are,
however, only temporary and are reversed within days9.
3. Hazard Control
Adequate control can be achieved by well-designed anaesthetic equipment10 and high standards in
scavenging11 and general ventilation12. Modern anaesthetic techniques should reduce exposure to a
minimum and anaesthetists, engineers and all other health and research staff should be involved in a
strategy for continuing effective control. It is important that new staff are instructed and trained to
achieve this strategy.
In some areas control measures cannot be as effectively applied, and it can be predicted that
exposures are likely to be greater in paediatric surgery, midwifery, dentistry and day case surgery (e.g.
urology).
4. Assessment
Unit General Managers/ NHS Trust Chief Executives/ Service Group General Managers and Heads of
Schools should be satisfied that the following factors are actively being considered in areas where
anaesthetic gases are used.
5. Ventilation
The Department of Health, in Engineering Sheet DV413 and Health Building Note No. 2614, recommend
a minimum supply of air of 0.65 m3/sec in anaesthetic rooms. In recovery areas ventilation to achieve 15
air changes per hour should be provided and, where new ventilation systems are being installed, extract
points should be located near to the head of every recovery bed.
In Dentistry and Midwifery, where anaesthetic agents including Entonox are used, rooms should be well
ventilated with a minimum of 5 air changes per hour as, recommended by hospital building note
No. 2115.
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In research areas the Home Office Code of Practice recommends 15-20 air changes per hour for fully
stocked rooms. Rates below this are acceptable where stocking density is low.
6. Scavenging
Active gas scavenging is recommended and reference should be made to BS6834, 1987. All new
equipment should meet this standard, and existing equipment should be assessed and if not
satisfactory priority should be given to replacing it. A visual flow indicator is an essential requirement for
monitoring scavenging equipment, and this is present in all systems. Anaesthetic practice that
minimises environmental contamination by only turning on nitrous oxide and volatile agents when the
patient is connected to the breathing system is desirable. The administration of oxygen from a facemask
at the end of anaesthesia will mean that expired gases will enter the scavenging system. Anaesthetic
gas delivery systems should be capped off at the end of an anaesthetic so as to prevent the
impregnated vapours in the breathing hoses from polluting the environment.
7. Maintenance Schedule
Anaesthetic equipment, gas scavenging, gas supply, flow meters and ventilation systems must be
subject to a planned preventative maintenance (PPM) programme. At least once annually the general
ventilation system and the scavenging equipment should be examined and tested by a responsible
person5,16 as recommended in BS6834.
8. Monitoring
All sites where anaesthetic gases are used should have an initial assessment when all the information
about the equipment used and any past atmospheric monitoring conducted is collected and
documented using the COSHH assessment form. Additional factors such as the extent and frequency of
gas use, the methods employed and the number of persons involved will also have to be taken into
consideration. In areas where anaesthetic gases are administrated infrequently, e.g. radiology, the
manager may request a COSHH assessment from a representative of anaesthetic or theatre staff.
Where there is no adequate records of any previous monitoring that would pertain to the current
circumstances a request should be made to the Occupational Safety, Health and Environment Unit,
UWCM for help and information. It may be possible in other areas where similar conditions apply, but if
not, hygiene assessment using general environmental and personal monitoring will need to be carried
out. Those responsible for routine checks should be clearly identified and a record kept. At least once
annually the general ventilation system and the scavenging equipment should be examined and tested
by a responsible person5,16.
9. Action Following Assessment
Action will depend on the environmental levels measured and the adequacy of equipment for delivery of
anaesthetic gases, the scavenging of exhaled gases and the general ventilation system. Where
exposures to greater than 100 parts per million of nitrous oxide have been recorded over an 8 hour
period, action will be required and, once taken, follow up hygiene measurements should be obtained.
Occupational Exposure Levels have been set for the main anaesthetic agents, see Appendix 2.
A new monitoring exercise should be conducted where new or refurbished premises have been
organised and there have been changes in equipment and ventilation. If there have been changes in
procedure, level of activity, or where any concern is expressed about the adequacy of waste
anaesthetic gas control, monitoring should be conducted.
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10. Staff Training
All staff should fully understand their responsibility to prevent unnecessary exposure to anaesthetic
gases. Information should be provided and an outline of a suitable handout is provided in Appendix 1.
11. Pregnancy
All staff working with anaesthetic agents and contemplating pregnancies should be advised that it is
sensible to limit exposure to toxic substances to the lowest level achievable. They should be given
information about the measures that have been taken to ensure safety, and those contemplating
pregnancies should be reassured that, were proper precautions in place, continuing employment in
areas where there is exposure to anaesthetic agents does not normally present a significant risk.
Anyone who has concerns that they wish to discuss privately can contact the occupational health
Department.
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12.
References
2.
Henderson, KA: Environmental Monitoring of Nitrous Oxide in Operating Theatres (1998), MPhil
3.
Protecting women of their jobs (1990),
Lancet, Vol. 336, Page 1289
4.
HSAC: Anaesthetic Agents: Controlling exposure under COSHH 1996
5.
Control of Substances Hazardous to Health regulations, 1999
6.
Yagiela, JA: Health Hazards and Nitrous Oxide: A Time for Reappraisal (1991),
Anaesthetic Progress, 38: 1-11
7.
Wilson, CW; McEachern, M: The Effects of Waste Anaesthetic Gases (1985),
Canadian Operating Room Nursing Journal; 13-20
8.
Sweeny, B; Bingham, RM; Amos, RJ; Petty, AC; Cole, PV:
Toxicology of bone marrow in dentists exposed to nitrous oxide (1985),
British Journal of Anaesthesia, 291; 567-569
9.
Kano, Y; Sakamoto, S; Sakuraya, K; Kubota, T; Hida, K; Suda' K; Takaka, F:
Effect of nitrous oxide on human bone marrow cells and its synergistic effect with
methionine and methotrexale on functional folate deficiency (1981),
Cancer Research; 41: 4698 - 4701
10.
BS 4272, Specification for anaesthetic and analgesic machines, Part 3 - continuous flow
anaesthesia machines
11.
BS 6834, Specification for active anaesthetic gas scavenging systems (1987)
12.
DHSS (1976), Health Circular, HC(76)38 - Pollution of operating departments etc. by
anaesthetic gases
13.
DHSS Engineering Data, DV4.1, February 1983
14.
Health Building Note No. 26, Operating Departments, February 1988
15.
Health Building Note No. 21, Maternity Departments, DHSS, 1987
16.
HSE Guidance Note EH42, Monitoring strategy for Toxic Substances
17.
UWCM COSHH Assessment Form
1.
Grey, WA: Occupational exposures to nitrous oxide in four hospitals (1989),
Anaesthesia, 44. 511-514
Further Information
1.
Health and Safety Guidance Note MA6, Occupational Health Aspects of Pregnancy
2.
ANHOPS (The Association of NHS Occupational Physicians):
Pregnancy and Employment in the NHS, 2nd Edition, 1991, Page 3
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Appendix 1
Guidance For The Safety Of Employees
Exposed To Anaesthetic Gases & Vapours
Staff Advice Note
Important Health And Safety Information
For Employees Who Work With Anaesthetic Gases
Inhalation anaesthetics are essential materials used in hospitals to induce unconsciousness in patients
prior to surgical procedures. The most commonly used agents are Nitrous Oxide, Halothane, Enflurane
and Isoflurane. Nitrous Oxide is also a good analgesic for pain relief during childbirth and some dental
procedures.
Health Effects
Concern has been expressed about the potential effects of long-term exposure to inhalation of
anaesthetics during pregnancies and some studies undertaken in the 1970s reported an increased rate
of spontaneous abortion in those exposed. More recent studies, including a major UK retrospective
study co-ordinated in Glasgow University, have not confirmed these earlier findings and it is generally
thought that these risks are of less importance than previously thought.
Controlling Exposure
Recognising that some employees are still expressing concern, the Health Services Advisory
Committee set standards for the main anaesthetic agents, setting a target for environmental control.
These Occupational Exposure Standards became operational in January 1996.
Action
An effective programme for controlling anaesthetic gases will be set up to ensure:
 A high standard of efficient ventilation in theatres
 Use of well maintained scavenging systems wherever possible
 Use of anaesthetic techniques which keep exposure to a minimum
 Staff are aware of their own responsibility in limiting theatre pollution
 Filling or emptying of funnel filled vapourisers to be performed in a well ventilated area
These arrangements will be monitored by means of regular maintenance checks and direct
measurement of the levels of anaesthetic gases in the working environment, which can be compared
with published standards. The results of these monitoring arrangements will be accessible to
employees on request.
Will These Arrangements Protect My Health
The programme outlined represents the best practice available and based on current information these
arrangements will ensure the health and safety of all employees workings with anaesthetic gases,
including those who are pregnant or contemplating pregnancy.
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What Do I Do If I Still Have Concerns About My Health In Relation To Work
Often your local manager will be able to provide further information which may solve the problem. The
staff in the Occupational Health Department are also willing to discuss any worries or concerns and you
may approach them in complete confidence.
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Appendix 2
Guidance For The Safety Of Employees
Exposed To Anaesthetic Gases & Vapours
Occupational Exposure Standards Fot Anaesthetic Gases
Hsac 1996
Enflurane
Halothane
Isoflurane
Nitrous Oxide
Sevoflurane
Desflurane
50 ppm
380 mg m3*
10 ppm
80 mg m3*
50 ppm
380 mg m3*
100 ppm
180 mg m3*
20ppm (recommended limit, Abbot
Laboratories)
No limit set
* Based on 8 hour Time Weighted Average (TWA) based on personal exposure.
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Appendix 3
Guidance For The Safety Of Employees
Exposed To Anaesthetic Gases & Vapours
Hazard Control Sheet - Anaesthetic Gases (Example)
Location:
University Hospital of Wales
Safety Audit:
Anaesthetic Gases and Vapours
Areas To Be Monitored:
Main Theatres and Recovery Room
Hazard Control Measures:
In Relation To:
1.
2.
3.
4.
5.
6.
Ventilation
Gas Scavenging
Maintenance
Anaesthetic Equipment
Personal Monitoring
Staff Training
Guidance Notes
1. Ventilation:
Actioned By: Estate Maintenance
Department of Health Engineering sheet DV413 and Health Building Note No. 2614 recommend a
minimum supply of air of 0.65 m/sec to be maintained in the theatre and 0.15 m/sec in anaesthetic
rooms.
In recovery areas ventilation should achieve 15 air changes per hour.
Extract points should ideally be located near the head of each recovery bed.
2. Gas Scavenging:
Actioned By:
Anaesthetist
RASS
Estate Management
Medical Physics
Theatre Manager
Health & Safety Adviser
Active gas scavenging is recommended and reference should be made to BS 6834:1987. All new
equipment should meet this standard, and priority should be given to the replacement of old equipment
that does not meet the standard.
A visual flow indicator is an essential requirement for monitoring scavenging equipment, is present on
all systems and should be ON during use.
The transfer of waste gases and vapours from a ventilator or breathing system is the responsibility of
the theatre staff. Respiratory and Anaesthetic Support Services (RASS) are responsible for the
'receiving unit' and the Estates Department for the 'disposal section' of the scavenging system.
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Those responsible for connecting the receiving unit to the disposal section should check the visual flow
indicator.
3. Maintenance Schedules:
Actioned By:
Theatre Management
Ventilation systems, gas scavenging and visual flow indicators should be checked at least once
annually by a nominated responsible person as recommended in BS 6834.
4. Anaesthetic Equipment:
Actioned By:
Anaesthetist
RASS
Estate management
Medical Physics
Theatre Manager
Health & Safety Adviser
All equipment in design and manufacture should comply with current British Standard specification and
should be inspected and tested to the laid down standards at the specified time intervals.
Arrangements will be made to ensure that inspectors are co-ordinated to interface with Estate
Department engineers' annual ppm checks.
5. Monitoring:
Actioned By:
Theatre Manager
Where background levels of anaesthetic and other gases have not been established, steps should be
taken to arrange for environmental and/or personal sampling to be conducted. On receipt of survey data
action should be taken to correct any deficiencies in plant and equipment or operational techniques.
6. Staff Training:
Actioned By:
Estate Management
RASS
Medical Physics
Theatre Manager
Health & Safety Adviser
All staff - medical, nursing, scientific and technical - should fully understand their responsibility to
prevent unnecessary exposure to anaesthetic gases.
Those responsible for staff training and for equipment and engineering plant checks should keep
detailed records of training undertaken and of the dates on which routine maintenance checks have
been carried out.
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Appendix 4
Guidance For The Safety Of Employees
Exposed To Anaesthetic Gases & Vapours
Bs 6834:1987 Definitions Used By
British Standards Council
Scope Of The British Standards
The British Safety Council (BS 6834:1987) specifies minimum performance and safety requirement for
active anaesthetic gas scavenging systems and their component parts intended to reduce the exposure
of hospital personnel to anaesthetic gases and vapours.
This standard covers systems which convey expired and/or excess anaesthetic gases from patient
breathing systems connected to anaesthetic machines and patient ventilators out of the room, e.g. the
operating theatre. It does not apply to the collection of gases by a proximity system, i.e. an anaesthetic
gas scavenging system which is not connected directly to the breathing system, nor to passive
anaesthetic gas scavenging systems.
Definitions Used In The British Standard
Anaesthetic Gas - a gas and/or the vapour of a volatile agent used in anaesthesia.
Anaesthetic Gas Scavenging System (AGSS) - a complete system which conveys expired and/or
excess anaesthetic gases from the breathing system to the exterior of the building(s) or to a place
where they can be discharged safely, to a non-recirculating exhaust ventilation system.
Transfer System - that part of the anaesthetic gas scavenging system (which may incorporate tubing)
which transfers anaesthetic gases from the exhaust port of the breathing system to the receiving
system.
Receiving System - that part of the anaesthetic gas scavenging system which includes an air-break
device and which receives gases from the exhaust port of the breathing system either directly or via the
transfer system.
Disposal System - that part of the anaesthetic gas scavenging system in which a gas flow is generated
which conveys the waste anaesthetic gas from the terminal unit pocket(s) of the scavenging system to
the exterior of the building(s) or to a place where gases can be discharged safely, e.g. to a nonrecirculating exhaust ventilation system.
Active Anaesthetic Gas Scavenging System - an anaesthetic gas scavenging system in which the
gas flow in the disposal system results from a powered device.
Air-break Device -
atmosphere.
a pressure limiting device comprising ports continually open to ambient
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AGSS Probe - a male connector used to connect a receiving system to the terminal unit socket of a
disposal system.
AGSS Terminal Unit Socket - the inlet to a disposal system which accepts and retains the AGSS probe.
Adjustable Pressure-Limiting (APL) Valve (of a Breathing System) - a pressure-limiting valve which
releases gas over an adjustable range of pressures. Its purpose is to allow for:
(a) the control of the breathing system pressure and thus of the intrapulmonary pressure;
(b) the release of expired and/or excess anaesthetic gases and vapours.
Breathing System - those gas pathways continuously or intermittently in communication with the
patient's respiratory tract during any form of ventilation. Where a shrouded APL valve is used to collect
gases from the source of their emission, the breathing system terminates at that valve.
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