On May 24, 2025, about 1020 local time, the sludge vessel Hunts Point was moored at the North River Wastewater Treatment Plant on the Hudson River, in New York, New York, when an explosion occurred aboard the vessel, killing one crewmember and injuring three others. There was no pollution from the incident, however, the vessel damage exceeded $10 million.
A 288.7-foot-long liquid cargo vessel (sludge vessel) called Hunts Point ended up built in 2014. New York City Department of Environmental Protection (NYC DEP) owned and operated the vessel.
The Hunts Point was one of five sludge vessels in the Marine Section of the NYC DEP that transported liquid sludge each day from six wastewater treatment facilities to the Wards Island Wastewater Treatment Plant, located on the East River in New York.
The Hunts Point had six cargo tanks and could transport up to 140,000 cubic feet (1 million gallons) of liquid sludge as cargo. Internal deep well pumps within the Hunts Point cargo tanks moved the sludge from the vessel to the dewatering facility.
Each tank had a radar level gauge and a pressure gauging system to measure the level of the cargo within the tanks. In addition, to reduce the smell associated with the sludge, the vessel had an odor-control air system that removed the air from each tank and sent it through a charcoal filter to exhaust vents, located on the king post near the bow.
The Hunts Point had gas detectors on the cargo deck area and throughout the vessel to notify the crew of a high concentration of flammable gas. There were also flammable-gas detectors located at NYC DEP facilities that processed wastewater/sewage.
Started Journey
On May 24, 2025, at 8:18 a.m., the Hunts Point departed the Wards Island Wastewater Treatment Plant, where it docked when not in operation, with a crew of six, including a master, chief engineer, assistant engineer, a mate, and two able seamen. The vessel was enroute to the North River Wastewater Treatment Plant to load about 100,000 cubic feet of liquid sludge, a transit that would take about 2 hours.
When the vessel departed Wards Island, about 40,000 cubic feet of cargo evenly distributed cargo remained in the cargo tanks from the previous day’s operation due to time constraints at the facility and the consistency of the sludge.
Because sludge remained within the tanks, it had become too viscous for the vessel’s cargo pumps to move it from the tanks to the facility. To reduce the thickness and make the sludge easier to pump, the crew had to complete a process called “innage reduction,” wherein they used water from the dockside fire main hydrant connection or from the vessel’s fire pump to add water via a fire hose into each of the six tanks.
Hunts Point on July 7, 2018, years before the explosion.
Source: Frank Joniak, shipspotting.com
The vessel’s permanent crewmembers told investigators the last time the tanks required this procedure was about 2020.
As designed, each tank had a cleaning hatch cover with 16 bolts. To perform the innage reduction process, all 16 bolts securing each of the six covers would end up removed and a crewmember would have to add water with the fire hose at each tank, one at a time.
Modified Cover
Shortly after the vessel started up in 2014, the chief engineer, who had been sailing on Hunts Point since it started operating, modified the cleaning hatch cover of each cargo tank to reduce the time required to add water during the innage reduction process. He drilled multiple holes into the center of each cleaning hatch cover to direct water into the tank. A carbon steel, four-bolt, 2.5-inch NPT (female) threaded flange secured to the hatch cover over the drilled holes and fitted with a threaded pipe plug.
The alteration changed the innage reduction process.
To complete innage reduction using the modified hatch covers, each cover’s pipe plug ended up removed, a fabricated 2.5-inch external pipe threaded into the flange, and a fire hose was connected to the pipe via an adapter. This enabled water to end up directly sprayed into each tank, via a fire hose connection, without the need to remove the hatch cover. When not in use, they secured the flange opening with the pipe plug.
No. 2 port cargo tank cleaning hatch cover after the explosion, showing burn/scorch marks indicating area where a broken bolt was removed and where a bolt was being heated by the torch when the explosion occurred.
Source: NTSB
The Hunts Point was the only NYC DEP vessel with this specialized modification to the cleaning hatch covers.
Rusted and Seized Plugs
Since it had been about 5 years since the last innage reduction process on the Hunts Point, all of the pipe plugs (connected to the flange) suffered from heavy rust and ended up seized, preventing their removal.
During the first hour of the voyage, the chief engineer was preparing for the innage reduction process, and the assistant engineer was standing watch in the engine room. When the assistant engineer went out on deck at the start of the second hour of the voyage, he noted, instead of removing the pipe plug, the chief engineer removed the four flange bolts threaded into the cleaning hatch cover for the no. 3 port and starboard, no. 2 starboard, and no. 1 starboard cargo tanks. A majority of the carbon steel bolts on the no. 1 and no. 2 starboard tanks had broken so the threaded part of the bolt remained in the cleaning hatch covers.
The assistant engineer, who normally worked on another NYC DEP vessel, told investigators he assumed each plug rusted in place, preventing them from being removed. He also stated he assumed the chief engineer’s plan was to bring all six flanges to the engine room, where they could mount the flanges in a workbench vice to make it easier to free the plugs.
Before the chief engineer left to take the watch in the engine room, he directed the assistant engineer to remove the flanges still attached to the cleaning hatch covers. The assistant engineer attempted to remove the flange for the no. 1 port cargo tank, but all of the bolts snapped, leaving the threaded sections of the bolts in the cleaning hatch cover.
Removing Bolts
The assistant engineer told investigators they had to remove the broken bolts from the cover so the flange could end up attached and secured for the innage reduction process. He said the rusted condition of the bolts made removing the broken parts from the hatch very difficult.
While the assistant engineer continued to work on removing the bolts, the vessel docked, starboard side to the North River Wastewater Treatment Plant, at 9:54 a.m. The mate and the two able seamen worked with facility personnel to attach the loading hose from the facility to the cargo tank pipe manifold. The mate and the two able seamen then went to the cargo control room, located on the main deck, to monitor the loading.
In preparation for cargo operations, the crew turned on the odor control air system for all of the cargo tanks. In addition, they started the ballast pump to remove water from the vessel’s ballast tanks as the cargo (sludge) was loading. Once they completed these tasks, the facility started to load sludge into the no. 1 port and starboard cargo tanks.
As cargo operations proceeded, the assistant engineer and chief engineer met in the cargo control room, and the chief engineer directed him to go to the engine room to get a pipe wrench and locking pliers. The chief engineer informed the assistant engineer he was going to his stateroom; the assistant engineer went to the engine room to retrieve the tools.
Left to right: Simplified diagram showing the typical arrangement for the innage reduction process and the modifications to the cleaning hatch cover.
Source: NTSB
Torch Warning
The master, who normally worked on another DEP vessel, departed the wheelhouse and went to the galley after cargo operations began. While there, he saw the chief engineer heading out on deck carrying various tools, including a propane torch.
According to the master, he spoke to the chief engineer as he walked by and told him twice not to use the torch out on deck. The master told investigators the chief engineer did not respond to him the first time but did respond, “Ok” the second time.
As the assistant engineer was about to head back to the main deck, the master stopped him and spoke to him about the chief engineer using the torch out on deck.
The master asked the assistant engineer to remind the chief engineer not to use the torch by the cargo tanks.
After the assistant engineer went out on deck, he saw the chief engineer sitting cross-legged aft of the cleaning hatch cover for the no. 2 port cargo tank. The assistant engineer approached and then squatted over no. 2 port cargo tank cleaning hatch cover by the chief engineer and removed a broken bolt with the locking pliers.
As the assistant engineer was removing the broken bolt, he saw the chief engineer light the torch and start to heat one of the other broken bolts. A second or two after the chief engineer started to heat the broken bolt, a yellow flame appeared above the holes drilled into in the cleaning hatch cover.
’Whistle’ Noise
After seeing the flame, the assistant engineer heard a “whistle” noise and then a rumbling noise from within the cargo tank no. 2 port. This prompted him to move away from the hatch cover by dropping backward to his right and rolling to the deck toward the centerline of the vessel.
The master and other crewmembers, who were in the house located aft on the vessel, heard a “hissing” noise and felt the vessel vibrate. At 10:20 a.m., an explosion occurred in the no. 2 port cargo tank.
Following the explosion, there was no fire; however, sludge burst out of the tank and covered the assistant engineer and the exterior of the vessel. The crew went out on deck to investigate and found the deck above the no. 2 port cargo tank had expanded upward during the explosion. Crew members found the assistant engineer, injured but conscious. The chief engineer was not on deck.
The master notified the dispatch at the NYC DEP office. He requested the NYC DEP notify the New York City Fire Department and the Coast Guard Sector New York Command Center of the explosion and the chief engineer was missing. The North River facility personnel stopped cargo operations and assisted the Hunts Point crew with searching for the missing chief engineer.
Before the arrival of the fire department at 10:30, they found chief engineer between the concrete dock and a wooden fender located on the starboard side of the vessel. The chief engineer ended up declared dead at the scene. The assistant engineer, master, and an able seaman sustained minor injuries and went to the hospital for treatment.
Procedures Mandated
After the casualty, the NYC DEP issued an intradepartmental memorandum, dated June 23, 2025, directing all personnel to review and comply with the following procedures and policies from the NYC DEP’s “Marine Operations Policy and Procedures:”
— 8.5—Hot Work, which contains procedures for obtaining a hot work permit as well as precautionary measures that must be taken for any hot work to be performed on a vessel.
— 8.7—Job Safety Assessment, which provides the process for identifying different types of hazards, risk levels, and precautions to be taken before beginning any type of work.
The NTSB determined the probable cause of the explosion on board the sludge vessel Hunts Point was unapproved hot work being conducted above a tank that contained a cargo that produced flammable methane gas, resulting in the gas igniting and the subsequent over pressurization of the cargo tank.
Click here for more on the report.