A newly surfaced video showing Navy SEAL recruits being tear-gassed is adding to scrutiny over the elite military unit’s training practices.

CBS News on Tuesday broadcast video that showed SEAL candidates being blasted with tear gas and ordered to sing “Happy Birthday” so they could not hold their breath. It was recorded last year on San Clemente Island near San Diego, the network reported.

The video shows the group of recruits crying out in pain and one man appearing to lose consciousness, which can happen when someone holds their breath while being tear-gassed. 

Preparing for tear gas exposure is a standard part of Navy SEAL training, but regulations say instructors should stand at least six feet away when spraying it to avoid giving burns and for should spray the gas for no more than 15 seconds, CBS reported. In the video, the spraying persists for more than a minute.

In a statement sent to Spectrum News on Wednesday, Rear Adm. Keith B. Davids, commander of the Naval Special Warfare Command — which oversees the SEALS — said the actions in the video are under investigation.

Davids said the conduct “raises questions about adherence to protocols and the lawfulness of the behavior.”

“Let me be clear - we have absolutely zero tolerance of hazing, abuse, or deviations from safety protocols,” Davids said. “As Navy SEALs, we serve our fellow Americans. Uncompromising integrity is our standard. Our character and honor are steadfast. Most of all, we are expected to lead by example in all situations.”

According to CBS News, the investigation will examine whether instructors were not aware of the proper procedures for tear gas training or whether they intended to abuse the recruits, which would be a criminal offense.

The video was first obtained by investigative reporter Matthew Cole, author of the book “Code Over Country” about Seal Team Six. He told CBS that SEAL candidates “felt that the instructors and the SEALs were abusive and very careless with their health.”

The video comes as an independent investigation, launched by the Navy, is reportedly underway into the selection course for SEALs following the death of 24-year-old Seaman Kyle Mullen in February, just hours after he completed the unit’s “Hell Week” test. The official cause of Mullen’s death was bacterial pneumonia, but his family blames the course.

The 5½-day Hell Week, the toughest training in the military, pushes SEAL hopefuls to their physical limits in cold, wet and grueling conditions, much of it done on little sleep. Its goal is to test their physical endurance, mental toughness, and pain and cold tolerance. On average, about one in four candidates pass the test, according to NavySEALS.com.

The order by Adm. William K. Lescher, the outgoing vice chief of naval operations, to open the investigation was issued in late August, one day after The New York Times reported Mullen’s death had exposed a number of problems at the selection course, known as Basic Underwater Demolition/SEALs, including a culture in which serious injuries and illnesses are viewed as weakness and a rise in the use of illicit performance-enhancing drugs to pass the course.

The Navy found syringes and PEDs inside Mullen’s car, according to multiple reports. The sailor’s mother, Regina Mullen, however, told CNN the toxicology report found no sign of PEDs in his system. She added that her son had told her that other trainees were using drugs.

CNN reported last week that senior Navy officials have asked the Defense Department to approve blood testing to detect potentially illegal or banned substances used in the elite forces.