Two young children ages 7 and 9 died after a scuba diving accident in a family swimming pool in Jensen Beach, Florida on April 23, 2021. The siblings were with a parent who was visiting friends at the home, reported ABC affiliate WFTS.

Both kids, whose parents were experienced technical divers, were described by their father as proficient swimmers and “proficient scuba divers”. They were given permission to use a scuba tank unsupervised in a swimming pool while the adults left the area to look at another piece of equipment in the garage. Approximately ten minutes later, the adults returned to the pool area to discover both children unconscious at the bottom of the pool. CPR was attempted and an ambulance was called. It was too late; despite all attempts to revive them, both children died three and a half days later.

So what happened in this incident? Was it simply a case of panic and drowning, or something else at play?

During the subsequent investigation, the air from the tank the children were breathing on was analyzed by the father, in the presence of the Martin County’s Sheriff department. It is believed that the tank they used was filled with helium instead of air. It is not known if the cylinder was labelled as such.

“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.”

Helium is often used in technical diving as one component of trimix (a mix of three gasses) to reduce the amount/concentration of oxygen in the mix. Helium is easy to breathe, is colorless, odorless and tasteless. It also results in rapid unconsciousness when breathed alone. A hypoxic mix such as “10/50” is used for deeper diving, as a bottom gas only, and cannot safely be breathed at shallow depths where the PO2 is less than 0.18 bar. It’s unknown if the tank the children used was filled with 100% helium or a mix.

The tragic accident is still under investigation.