Thirty-three passengers and one crew member were killed during the Labor Day 2019 diving boat excursion
The dive boat Conception is engulfed in flames after a deadly fire
Conception boat fire
| Credit: AP/Shutterstock

The owners of the California diving boat that caught fire last year, killing 34 people, are at fault for the tragedy, as it was on their watch that all required watchmen were asleep when the blaze broke out, federal safety officials said.

The National Transportation Safety Board announced Tuesday that the “probable cause of the fire and subsequent sinking” of the Conception diving boat was the failure of Truth Aquatics, as the company failed to enforce certain rules that in turn allowed the blaze to grow undetected.

Thirty-three passengers and six crew members were on board the Conception on Sept. 2, 2019 when the boat caught fire around 3 a.m. off the coast of Santa Cruz Island. Five crew members who were asleep on the boat’s uppermost sun deck survived, while the one crew member sleeping alongside the passengers in the bunkroom on the lower deck did not.

Though the surviving crew members were awoken by noise and attempted to alert those below to the blaze, their efforts were blocked by fire and smoke, and all victims became trapped and died of smoke inhalation, according to the NTSB.

RELATED VIDEO: Mayday Audio Raises Questions About Circumstances in Dive Boat Fire — Were Passengers Trapped?

The NTSB said that the lack of a required roving patrol that night likely delayed initial detection of the fire and allowed it to grow, which hampered efforts to quell the flames and evacuate the passengers and “directly led to the high number of fatalities in the accident.”

“I hate the term accident in this case because, in my opinion, it is not an accident if you fail to operate your company safely,” board member Jennifer Homendy said at a virtual hearing on Tuesday, the Associated Press reported.

Though the vessel had passed all Coast Guard inspections, the NTSB said that the Conception did not have the Coast Guard regulatory requirement for smoke detectors in all accommodation spaces, and also had inadequate emergency escape arrangements, as both escape routes led to the same compartment, which was engulfed in flames.

Boat Fire California
Conception on fire
| Credit: AP/Shutterstock

The NTSB said that in response, it was calling for major safety improvements to small passenger vessels, including a requirement for interconnected smoke detectors in all passenger areas and a push for the Coast Guard to put a new inspection program in place that could better verify the use of required roving patrols.

Improvements would also include a recommendation that vessels have a secondary means of escape that ideally lead somewhere other than the primary exit in case a fire blocks the path, as it did on the Conception.

“The Conception may have passed all Coast Guard inspections, but that did not make it safe,” NTSB Chairman Robert L. Sumwalt said in a statement. “Our new recommendations will make these vessels safer, but there is no rule change that can replace human vigilance.”

Boat Fire California
Credit: Ringo H W Chiu/AP/Shutterstock

The Conception did have smoke detectors in the below-deck area, but they were not connected to each other, and there were no smoke detectors in the common area above the sleeping quarters, the NTSB said.

Investigators believe that that common area is where the fire began, though its exact cause and origins remain unclear due to the extensive damage the boat endured during the blaze.

The Coast Guard told Reuters in a statement that the NTSB’s recommendations would be “carefully” considered “through a deliberate process, which will include review by all subject matter experts and senior leaders responsible for implementing the potential regulatory changes.”

Attorneys for Truth Aquatics did not immediately respond to PEOPLE’s request for comment.