NHS Resolution has settled 121 claims from maternity staff at Basildon Hospital for a total of £735,000 after they were exposed to excessive levels of nitrous oxide, also known as Entonox. The claims included 85 midwives, and staff reported fatigue, anxiety, headaches and “brain fog” after working long shifts in the maternity unit over months and years.
An internal review found that some workers were exposed to concentrations up to 30 times the legal workplace limit between 2021 and 2023. Staff were not told for 16 months about test results commissioned by the trust that showed exposure levels had exceeded safety thresholds. The Royal College of Midwives described the legal action as the largest group claim brought by midwives in the UK; NHS Resolution said some claims remained outstanding, while the college said one claim had yet to be settled.
The incident became public after air testing identified potentially high nitrous oxide levels in October 2022. The hospital said it ventilated the area, arranged further testing and briefed staff. When levels remained unacceptable, Entonox use was suspended from early December until 20 December, alternative pain-relief arrangements were offered and 12 women chose to give birth elsewhere. NHS England, the Care Quality Commission and the Health and Safety Executive were informed, and the HSE began an investigation.
A later independent review found weak governance, problems managing medical gases, instability in leadership, inadequate openness during the response and a need for more occupational-health resources. The trust apologised, acknowledged that it should have acted faster and said it had strengthened oversight of medical-gas monitoring. It also installed scavenging equipment in the maternity unit and said current nitrous oxide levels were within safe limits for patients and staff.
The Royal College of Midwives raised concerns with the HSE, wrote to NHS trusts in England about the risks and worked with the regulator on updated guidance for Entonox. The compensation resolves most of the claims, but the HSE investigation and remaining legal matters continue to form part of the incident’s follow-up.