An international Delta flight recently made a U-turn due to a passenger’s severe case of diarrhea, which was deemed a 'biohazard'

A Delta flight from Atlanta to Barcelona made national news after it was diverted due to a passenger's case of severe diarrhea last Friday. In a clip from an emergency call to dispatchers shared on social media, the pilot called the incident “a biohazard issue.”

Accidents involving bodily fluids on planes don’t typically force the flight to make a U-turn. So, what constitutes a biohazard significant enough to reroute a plane? PEOPLE consulted industry professionals and the airlines' regulating agencies to find out.

Robin Mermelstein, a Miami-based flight attendant who’s worked for a major airline for 40 years, tells PEOPLE she’s never been on a flight that turned around due to a biohazard — though her flights have made unplanned landings for medical emergencies after an on-call physician was consulted.

Related: Delta Flight Diverted After Passenger Suffers Severe Case of Diarrhea

Mermelstein, 63, says she’s worked on flights where passengers have vomited in their seats. But in those cases, airline staff are trained to use a biohazard fluid control powder called Red-Z that is poured over vomit to dissipate it, which she calls “amazing.”

“It just goes away,” she says. “But I think that [Friday's Delta episode] is probably one of those really, really uncommon isolated incidents. … Obviously, you just cannot have that.”

Mermelstein says she’s also been on flights where people have had “very bad” accidents in the airplane lavatory, but in the most extreme cases she's witnessed, she would just lock off that bathroom.

However, she notes the difference with what happened on the Delta flight was likely that the diarrhea, a trail of which can be seen on the floor of the cabin’s aisle in a video shared on social media, “was everywhere.”

“If [the passenger with diarrhea] was walking to their seat and just had an accident all over, and then you have the smell, obviously, if it's in that many places, I think that that is probably the worst.”

Related: Air Canada Issues Apology to 2 Passengers Escorted Off Plane After They Had to Sit in Seats Covered in Vomit

One commenter on Twitter (now known as X), who said their partner was on the Delta flight, reported that it “smelled horrible” and that vanilla-scented disinfectant used to mask the odor “only made it smell like vanilla s---.”

While Mermelstein says she has even seen parents change babies’ diapers in their seats, those incidents didn’t impact a common area of the aircraft cabin.

“This would affect everybody on that plane,” she says.

So what does constitute a diversion-worthy accident? It comes down to the pilot's judgement.

When asked about the process for diverting a flight, a spokesperson for the Federal Aviation Administration told PEOPLE: “The pilot in command is responsible for deciding how to respond to a situation and may work with airline dispatchers to develop a plan.”

The Delta flight, which left from Hartsfield-Jackson Atlanta International Airport at 8:29 p.m. on Sept. 1, finally landed in Barcelona eight hours after its scheduled arrival.

"Our teams worked as quickly and safely as possible to thoroughly clean the airplane and get our customers to their final destination,” Delta told PEOPLE in a statement when asked about the incident.

The airline added, “We sincerely apologize to our customers for the delay and inconvenience to their travel plans.”

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