given the relative ease and safety of administering 50% nitrous oxide as an analgesic. The rapid reversibility of its effect would also prevent it from precluding diagnosis. Recreational use Recreational inhalation of nitrous oxide, with the purpose of causing euphoria and/or slight hallucinations, began as a phenomenon for the British upper class in 1799, known as "laughing gas parties". Starting in the nineteenth century, widespread availability of the gas for medical and culinary purposes allowed the recreational use to expand greatly throughout the world. In the United Kingdom, as of 2014, nitrous oxide was estimated to be used by almost half a million young people at nightspots, festivals and parties. Widespread recreational use of the drug throughout the UK was featured in the 2017 Vice documentary Inside The Laughing Gas Black Market, in which journalist Matt Shea met with dealers of the drug who stole it from hospitals. A significant issue cited in London's press is the effect of nitrous oxide canister littering, which is highly visible and causes significant complaint from communities. Recreational users often misperceive nitrous oxide as a route to a "safe high", and are unaware of its potential for causing neurological damage. In Australia, recreation use became a public health concern following a rise in reported cases of neurotoxicity and a rise in emergency room admissions, and in (the state of) South Australia legislation was passed in 2020 to restrict canister sales. Safety Nitrous oxide is a significant occupational hazard for surgeons, dentists and nurses. Because nitrous oxide is minimally metabolised in humans (with a rate of 0.004%), it retains its potency when exhaled into the room by the patient, and can pose an intoxicating and prolonged exposure hazard to the clinic staff if the room is poorly ventilated. Where nitrous oxide is administered, a continuous-flow fresh-air ventilation system or scavenger system is used to prevent a waste-gas buildup. The National Institute for Occupational Safety and Health recommends that workers' exposure to nitrous oxide should be controlled during the administration of anaesthetic gas in medical, dental and veterinary operators. It set a recommended exposure limit (REL) of 25 ppm (46 mg/m3) to escaped anaesthetic. Mental and manual impairment Exposure to nitrous oxide causes short-term decreases in mental performance, audiovisual ability and manual dexterity. These effects coupled with the induced spatial and temporal disorientation could result in physical harm to the user from environmental hazards. Neurotoxicity and