The U.S. Navy is investigating an incident in California last year when SEAL recruits were exposed to tear gas.
CBS News obtained video showing the recruits on San Clemente Island being blanketed in a cloud of tear gas while being ordered to sing "Happy Birthday" so they couldn't hold their breath during training.
Although exposure to tear gas is a standard part of SEAL training, the video raises questions about how that training was carried out.
The video shows the gas lasting for more than a minute, and recruits crying out in pain. One recruit appears to pass out, which the regulations warn is what happens when you try to hold your breath.
"I think this type of training is really senseless," Sven Jordt, a Duke University associate professor who studies tear gas and its effects, told CBS News. "It looks more like a form of hazing."
The admiral in charge of Navy SEALs ordered an investigation into the incident and told CBS News that the video raises questions about "the lawfulness of the behavior."
The Navy's probe is examining whether the gas was administered at too close a range for too long, CBS News said.
The Navy also is looking into whether the instructors were unaware of the proper procedures, or whether they meant to abuse the SEALS, which could be a criminal offense.
Regulations for tear gas use in SEAL training require the instructors to stay at least 6 feet away from the recruits to avoid the danger of burns, and to use the gas for no more than 15 seconds.
The recruits in the video already had completed two-thirds of the selection course.
Nearly all military recruits deal with tear gas, usually when they're taught how to properly don a face mask.
CBS News said the video was obtained by investigative reporter Matthew Cole, author of "Code Over Country," a recent book about Seal Team Six.
"I got this video from some SEAL students who are trying to become SEALs and felt that the instructors and the SEALs were abusive and very careless with their health," Cole told the outlet.
The Navy last month ordered an investigation into the selection course after the death of SEAL candidate Kyle Mullen, who had just made it through "Hell Week."
Mullen died of pneumonia, which his mother attributed to the time he spent submerged in the cold water off the coast of Southern California, NJ Spotlight News reported.