Nasa has been forced to deny that there was an emergency situation on board the International Space Station (ISS), after an official livestream accidentally aired a medical drill which simulated a crew member in extreme medical distress, prompting alarm on social media. “There is no emergency situation going on aboard the International Space Station,” Nasa’s ISS account posted on X. “Audio was inadvertently misrouted from an ongoing simulation where crew members and ground teams train for various scenarios in space.” At 5.30pm CDT (10.30pm GMT) on Wednesday, footage from Nasa’s ISS livestream was replaced with a message that the feed had been “temporarily interrupted” and that the video would return when the “connection is reestablished”. Soon after, a person that appeared to be communicating with crew on board the ISS began to issue advice related to a serious emergency involving a “commander” who was experiencing decompression sickness. “So if we could get the commander back in his suit, get it sealed … for suited hyperbaric treatment … Prior to sealing, closing the visor and pressurising the suit, I would like you to check his pulse one more time,” the speaker, who identified herself as a flight surgeon working at the SpaceX mission control centre in Hawthorne, California. According to Nasa, flight surgeons are physicians with specialised training in aerospace medicine based at mission control centres. Hundreds of people were viewing the popular Nasa livestream on YouTube as the simulation continued and the “commander’s” situation appeared to deteriorate. “I am concerned that there are some severe DCS [decompression sickness] hits … unfortunately, the prognosis for commander is relatively tenuous,” the unnamed flight surgeon said. Several popular space accounts quickly drew attention to the incident on social media, with one user calling it “odd and disturbing”. Eric Berger, space editor at tech publication Ars Technica, called the broadcast “frankly scary”, while many others were quick to identify that it was likely a drill. SpaceX later clarified that what viewers heard was a test apparently taking place in California and that all training crew were “safe and healthy”. Nasa said the simulation was not related to any real emergency and the ISS crew members were in fact in their “sleep period” at the time the drill inadvertently aired. “All remain healthy and safe, and tomorrow’s spacewalk will start at 8am EDT as planned,” Nasa said in its statement.