More than 120 midwives and maternity staff at Basildon University Hospital have secured almost £750,000 in compensation after being exposed to dangerously high levels of nitrous oxide while at work.

The workers, including more than 80 members of the Royal College of Midwives (RCM), were exposed to the gas between 2021 and 2023 because of poor ventilation and leaking gas lines and equipment on the maternity unit.

Tests first identified dangerous levels of the chemical in June 2021, but staff were not informed until October 2022. Safety measures, including improved ventilation and guidance on taking regular breaks, were not introduced until 2023.

Many staff reported symptoms including fatigue, anxiety, headaches and brain fog.

Mid and South Essex NHS Foundation Trust admitted exposing workers to dangerously high levels of nitrous oxide following legal action brought by Thompsons Solicitors, working with the RCM. A settlement of almost £750,000 has now been agreed.

The RCM said the case was the largest group action ever brought by midwives in the UK and came as the organisation marked 50 years as a trade union.

Gill Walton, the RCM's chief executive and general secretary, said midwives had been exposed to dangerous levels of the gas for years while caring for women and babies.

"Even once the problem had been discovered, it was more than a year before staff were told. That is simply not acceptable and no midwife should ever be treated that way," she said.

Walton described the settlement as a landmark for members, adding that the case should serve as a warning to NHS employers about their responsibility to protect staff.

The RCM stressed that gas and air, also known as Entonox, remains a safe and important option for pain relief during labour when used appropriately. It said the risks in Basildon arose from prolonged occupational exposure and unsafe working conditions, rather than the pain relief itself.

The union also raised concerns with the Health and Safety Executive (HSE), which issued a notice of contravention against the Trust. The RCM has since worked with the regulator to update and improve guidance on Entonox use.

Daniel Poet, partner and disease specialist at Thompsons Solicitors, said: "Monitoring exposure levels should be routine in maternity settings. While we believe these extreme levels were confined to this one hospital, the case highlights why employers must act – and act fast – when warning signs emerge."