This page is aimed at those in maternity units who are responsible for preventing harm from high levels of exposure to nitrous oxide (gas and air). It covers:
Levels of exposure
Nitrous oxide is an invisible, anaesthetic gas used widely in healthcare. It is subject to the Control of Substances Hazardous to Health Regulations (COSHH).
A 50:50 mixture of nitrous oxide and oxygen is commonly used to help control pain, particularly in maternity units. This formula is commonly referred to as ‘gas and air’.
High levels of exposure can cause serious health effects, such as neurological problems and anaemia. This is due to the vitamin B12 in a person’s body no longer working.
Nitrous oxide has a long-term workplace exposure limit (WEL) of 100 ppm or 183 mg.m3 8-hour time weighted average (TWA).
Control measures
Risk of exposure to nitrous oxide should be established through a COSHH risk assessment of each space in which it is used.
Three main types of control systems are used in maternity departments to control the risk from nitrous oxide:
- a demand valve and mouthpiece or facemask used by the patient which captures exhaled breath, ensuring it is not released into the room
- an associated extraction or scavenging system with an extraction unit located close to the breathing zone of the patient
- general ventilation
The demand valve and mouthpiece or facemask system is the most effective method of control. This is because the exhaled air is not released back into the room, as long as the mouthpiece or facemask is not removed before the patient exhales.
General ventilation is least effective because it:
- is located at a distance from the source (exhaled air)
- relies on the effectiveness of the room ventilation
For these reasons, only using this approach is unlikely to achieve adequate control. If only general ventilation is used, dutyholders should:
- be able to explain why other systems are not in place
- provide evidence that control is achieved
To ensure the effectiveness of your control systems, keep them well maintained and have suitable training for their use.
Monitoring exposure
Monitoring may be appropriate for potential exposure to nitrous oxide. The level of monitoring should reflect:
- the activities carried out
- the number of workers who could be exposed
Not all potentially exposed people need to be provided with a sampling unit.
It is important that exposure monitoring for any airborne contaminant includes the relevant contextual information for each sample taken. For nitrous oxide in a maternity department, this would include:
- the time midwives and student midwives, doctors and/or support staff attend to the delivery of a child or children (the actual exposure time, assessed over a representative number of days)
- an estimate of the level of demand by the expectant mother
- any controls present, for example scavenging equipment
- any other information that is likely to affect the exposure levels, such as movement of people or other activities in the room
In most working environments, if an activity involves any exposure to hazardous substances it is typically over reasonably regular working hours – up to 8 hours a day, 5 days a week, with limited variability. However, this is not always the case in the healthcare sector, especially in a maternity unit where a pattern of working from 9am to 5pm would be unusual.
Exposure to exhaled gases like nitrous oxide in a maternity department is not uniform on any given day or over any given week. This means you will need competent interpretation and assessment of the measured data.
Evidence of competence
Exposure monitoring should be carried out by an appropriately competent person. Evidence of competence in this area can be demonstrated by:
- training with the British Occupational Hygiene Society (BOHS) or Faculty of Occupational Hygiene (FOH)
- gaining the associated qualifications, for example Measurement of Hazardous Substances M501
In addition, further modules would be appropriate in assessing control, for example Control of Hazardous Substances M505.
Any reports produced should be reviewed and audited by an appropriately competent person.
Management systems
There should be an effective management system in place for controlling the risk of exposure to nitrous oxide. This should include, but not be restricted to:
- appropriate protocols to deliver and implement effective control and exposure monitoring
- managing the risk, including details of the role and relevant competencies. This extends to any external competent advice that is engaged, for example a qualified occupational hygienist or occupational health professionals
- policies, procedures and arrangements for effectively managing the risks faced by staff who work with nitrous oxide. This should include consideration of workers who may be more vulnerable to the effects of exposure, such as those who are pregnant
- how success is to be measured, including action plans where necessary for delivery of control, and how the system ties into risk management processes, clinical governance and health and safety management
An occupational health physician may recommend biological effect monitoring, for example where there may be failing or deteriorating control measures.
You must consult workers or their safety representatives on all elements of any biological effect monitoring programme, for example:
- how potentially affected workers will be identified
- arrangements for gaining workers’ consent to provide samples and their processing by occupational health staff
- gaining specific consent for disclosing the results
- describing how workers will be managed if results suggest their exposure should be reduced
- any review of the programme