JENSEN BEACH, Fla. — Two young children died Tuesday after a possible drowning incident that occurred at home in Martin County on Friday, according to the sheriff's office.
Investigators said the victims, a brother and sister ages 7 and 9, were left unattended in a swimming pool just after 5 p.m. Friday, at a home in the Pinecrest Lakes community of Jensen Beach.
The siblings were with a parent who was visiting friends at the home.
The sheriff's office said the children were described by the parent as experienced swimmers and proficient divers and had been to this home on past occasions.
The brother and sister were given permission to use the pool, along with a scuba tank, while the adults conducted their business, according to the investigators.
Once the scuba tank was placed in the pool, the children followed, and the adults told detectives they walked away from the pool area into the garage to look at another piece of equipment.
After leaving for a short amount of time, an adult returned and found both children at the bottom of the pool. The tank was also found at the bottom of the pool.
The sheriff's office said several adults at the home immediately pulled the children from the pool and began CPR.
The children were transported to the hospital, but both died early Tuesday morning.
"If you're breathing 100% nitrogen or 100% helium, you're going to pass out," said Jim Abernathy, a local dive expert. "It'll happen very quickly. You won't even know."
Abernathy said the only tanks that contain helium are tri-mix tanks used for diving at extreme levels of depth.
"If you pass out on land you'll wake up, you'll be fine," said Abernathy. "Because you're still breathing air. Underwater you'll drown. The complication that put you there was no oxygen because you're going to continue breathing, you'll drown."
Authorities said the cause of death will be determined once an autopsy has been completed.
"It's looking like the children were not breathing the oxygen they believe they were breathing. It looks like they were indeed breathing helium. With helium, they would have the sense that they were actually breathing oxygen, so they would feel like they're breathing normally," said Major John Budensiek with the Martin County Sheriff's Office. "They wouldn't get the feeling that they would need to take a breath. So, they would have breathed helium, and because there is no oxygen in helium, ended up in the state that they were in."
Officials said the children lived in a neighboring county.
Detectives are working with the State Attorney's Office to investigate the case, including possible issues related to the dive tank that the children were using.