The sinking of MV Conception occurred on September 2, 2019, when the 75-foot (23 m) dive boat caught fire and eventually sank off the coast of Santa Cruz Island, California, United States.

[11] Federal and international regulations require boats over a certain size to be made of fire-resistant materials and to include fire sprinklers and smoke detectors wired into the ship's electronics or linked to the bridge.

The returning divers stowed flashlights, cameras, and photo strobes on the two aft tables in the salon; some of these were plugged in to charge alongside cellular phones and tablets.

Channel Islands Harbor Station personnel radioed the Ventura County Fire Department (VCFD) and requested Medic Engine 53 (the closest unit) to respond to the scene aboard a Coast Guard vessel which was preparing to leave.

[21]: 14  The SCC also coordinated the dispatch of USCGC Narwhal (WPB-87335), based in Corona Del Mar, and CG 6540, a HH-65 Dolphin helicopter which had been forward deployed to Point Mugu from Air Station San Francisco.

In addition, since Conception had drifted into shallower waters, most of the fireboats on-scene were unable to continue fighting the fire for lack of clearance, including a shallow-draft Santa Barbara Harbor Patrol boat.

[36] Although the two initial-response RB-Ms onsite had portable 250 US gal/min (950 L/min) dewatering pumps that could be used for firefighting, the VCFD determined they would not be effective, and they began searching the waters for survivors, as the magnitude of the fire aboard Conception meant there was no one left alive on board the vessel.

[34] In order to attempt to fight the fire and allow fireboats to reach the vessel, a grappling line was secured and the still-burning Conception was towed out to deeper water by Retriever II.

Conception was then towed by Retriever II back to shallower waters to aid in its recovery,[36] but the boat sank stern-first about four hours after the fire broke out[9] at 6:54 a.m.,[21]: 18  coming to rest upside-down at a depth of 64 feet (20 m) approximately 20 yards (18 m) from the north shore of Santa Cruz Island.

Via press release, Feinstein stated "It's inconceivable that with all the safety regulations we have in place today, a fire on a boat can lead to the loss of life we saw this morning near Santa Cruz Island".

[27] Conception had settled on the bottom upside-down; the first attempt to roll the boat upright and raise it was planned for September 6, but recovery efforts would be delayed if the windy conditions had continued.

[22] According to the Los Angeles Times, the preliminary investigation identified the lack of a roaming night watch as a safety deficiency,[75][76] in violation of the conditions in the vessel's Certificate of Inspection[16] and 46 C.F.R.

[64]: 62 Although the NTSB was not able to determine the definitive cause of the fire, the likely origin point was in the aft part of the salon, and the most likely sources included the electrical distribution system, unattended battery charging, or improperly discarded smoking materials.

"[80] Because of the pending criminal investigation of the fatal fire, the NTSB was requested to not interview the ship's captain, the first galley hand, or any Truth Aquatics employee responsible for operations.

[81] The Coast Guard issued MSIB 03–20 on February 6, 2020, recommending that small passenger vessel owners and operators voluntarily establish a safety management system to identify and mitigate potential hazards.

[82] A spokesman for the Coast Guard stated the agency had embarked on a concentrated inspection campaign for every small passenger vessel with overnight accommodations shortly after the preliminary results had been determined.

[81] The Coast Guard has not cited any owner, operator, or charterer with a violation or fine for failing to post a roving patrol since 1991, demonstrating the agency's failure to enforce the requirement.

Collectively, the NTSB called it "a habitual disregard for rules, policies, and procedures" and the resulting normalization of deviance could have been discovered earlier if Truth Aquatics "had been actively engaged in ensuring the safe practices required by regulations were being followed".

"[80] The NTSB reported "the [secondary hatch] escape path would have been challenging for anyone to navigate without practice and would have been further complicated by low lighting and poor visibility due to smoke from the fire.

[87] The ATF's investigation used burn tests simulated on a full-scale recreation of the vessel's main deck, and found that the flames would have blocked all escape routes soon after ignition, and any winds blowing would have spread the fire even more quickly.

The civil lawsuit, filed in Ventura County Superior Court against Truth Aquatics and Worldwide Diving Adventures, claimed the crew had not received proper training nor was the boat outfitted with appropriate emergency equipment.

[91][92][93] A counterclaim against the original limitation of liability suit was filed in November 2019 by the spouse of a passenger who died aboard Conception, seeking funeral expenses and wrongful death, survival, and punitive damages.

[111] California Governor Gavin Newsom issued a statement through Twitter praising the efforts of the emergency medical workers and offering his condolences to the families and loved ones affected.

[32] The United States House of Representatives Subcommittee on Coast Guard and Maritime Transportation held a hearing on November 14, 2019, to discuss commercial and passenger vessel safety.

[119] Brian Curtis, the director of the NTSB's Office of Marine Safety, testified before the Subcommittee, reiterating the investigation into the sinking of Conception was still in progress and that it would focus on the wreck itself as well as other factors such as current regulations, fire alarm and warning systems, evacuation routes, training, and company policies and procedures.

[121] In response, Timme vowed the Coast Guard would "wholly fulfill our regulatory oversight role to keep the maritime public safe" and would adopt new regulations immediately after they are published by an internal task force developing inspection rules for vessels similar to Conception.

[122] In December 2019, Rep. Salud Carbajal, whose district includes Santa Barbara, Rep. Julia Brownley, and Sen. Dianne Feinstein introduced the Small Passenger Vessel Safety Act of 2019 to mandate some of the recommended changes.

[98] In its 2020 report, the NTSB recommended the Coast Guard make revisions to Title 46 Code of Federal Regulations Subchapter T, governing small passenger vessels.

Recommended changes included stricter requirements for interconnected smoke detectors comprehensively deployed in all passenger accommodation spaces, development of an inspection procedure to verify that roving patrols are implemented, and secondary escape paths that provide an alternate exit point.

[64]: 53–54 As part of the National Defense Authorization Act, Congress directed the Coast Guard in December 2020 to review its fire safety regulations for small vessels that accommodated passengers overnight.