Investigating nitrous oxide leaks at St George Hospital: A case study using the discrepancy and pressure testing methods.

Nitrous oxide (N2O) is ozone-depleting and a greenhouse gas. Studies have shown a high wastage of N2O from leaking hospital infrastructure. Identifying leaks is a priority action in the Australian national health and climate strategy. Four possible methods to identify leaks have been described: the discrepancy method, cylinder weighing, pressure testing, and flow monitoring. We used the discrepancy and pressure testing methods to investigate possible N2O leaks at St George Hospital, a large tertiary hospital in Sydney providing medical, surgical, birthing, paediatric, and trauma care. Our investigation was in four steps: (a) to determine how much N2O is procured and calculate the associated carbon emissions; (b) to outline the location of pipeline supply; (c) to determine how much N2O is used clinically (operating theatres, delivery suite, other areas); and (d) to assess for leaks throughout the pipeline using pressure testing. We estimated a total annual 'worst case' estimate of maximum possible clinical N2O use of approximately 801,866 litres at St George Hospital in 2021, with 14,846 litres used in the operating theatres and 787,020 litres used in the delivery suite. This estimate was approximately 319,534 litres (or 28%) less than the 1,121,400 litres procured N2O used to supply the manifold, indicating leaks at least this large. Pressure testing of the full manifold system identified leaks in three operating theatres. A substantial amount of the N2O procured by St George Hospital is leaking to the atmosphere causing unnecessary emissions. This N2O provides no benefits to clinical care, has financial costs, and may pose potential occupational exposure risks to clinicians.