On Thursday, emergency divers were forced to cancel search and rescue operations around Baltimore’s Francis Scott Key bridge after officials observed a “sheen” of hazardous chemicals around the M/V Dali.

In a press conference late Wednesday evening, Jennifer Homendy, chair of the National Transportation Safety Board, confirmed that the cargo ship M/V Dali was carrying 56 containers of HAZMAT, or hazardous materials when it struck the bridge, Homendy estimated this was about “764 tons of hazardous materials” including “corrosives, flammables” and “lithium ion batteries.”

Early Tuesday morning just before 1:30 a.m., one of the three spans that comprise the Francis Scott Key Bridge collapsed upon being struck by the Dali after it appeared to lose power. Eight construction workers, from Mexico, Guatemala, Honduras and El Salvador, were working on the bridge when it suffered a catastrophic failure after being struck by the ship.

All eight of the workers were employed by Brawner Builders. Two of the workers were rescued alive on Tuesday, while the other six are presumed dead.

On Wednesday, divers discovered the bodies of two of the construction workers. Alejandro Hernandez Fuentes, 35, from Mexico, and Dorlian Ronial Castillo Cabrera, 26, from Guatemala, were found together in a red pickup truck about 25 feet below the water.

Fellow workers Maynor Suazo Sandoval, a husband and father from Honduras, and Miguel Luna, a father of three from El Salvador, have yet to be recovered. The last two missing construction workers have yet to be publicly identified or located. Besides the cold, dark waters, emergency divers were also contending with thousands of tons of debris, including sharp metal, from the bridge and containers that went overboard.

Part of the difficulty in locating the workers is the ongoing danger of chemical exposure. Chair Homendy confirmed on Wednesday that some of the containers the ship was carrying had been punctured and that officials with the NTSB had observed a “sheen” of chemicals on top of the water.

“Some of the Hazmat containers were breached, we have seen sheen on the waterway,” Homendy said. Questioned by reporters on the breach of the containers, Homendy replied, “federal, state and local authorities are aware of that and they will be in charge of addressing those issues.” She added that part of the ongoing NTSB investigation would be “documenting that type of release.”

On Thursday, multiple media outlets reported that the Unified Command, which is in charge of overseeing the response to the bridge collapse, had paused dive and recovery operations due to the hazardous conditions around the accident site. The Unified Command includes elements from the US Coast Guard, US Army Corps of Engineers, Maryland Department of the Environment, Maryland Authority, Witt O’Brien’s (a private corporation that specializes in “risk management and emergency response”) and the Maryland State Police.

Due the release of chemicals, the Unified Command has established a 2000-yard “Safety Zone” around the M/V Dali. Additionally, in an attempt to contain the spillage that has already occurred, emergency crews have already deployed 2,400 feet (731 meters) of absorbent boom. Investigators have been observed collecting water samples for testing.

While officials remain tight-lipped about the extent of possible chemical exposures, in their press conference Wednesday, Homendy of the NTSB confirmed that the Francis Scott Key Bridge was one of “17,468 fracture critical bridges in the Untied States.”

A “fracture critical” bridge, Homendy explained, means, “if a member fails that would likely cause a portion of, or the entire bridge to collapse. There is no redundancy.”

Newer bridges Homendy explained, have some sort of redundancy built in. “Whether that is transmitting loads to another member or some sort of structural redundancy. This bridge did not have redundancy.”

This begs the obvious question: why did the bridge not have any “redundancy” built into it over the last 40 years?

In an interview with Reuters, Erin Bell, chair of the College of Engineering and Physical Sciences at the University of New Hampshire, argued along these lines. “The construction code has got to do better,” she said.

Refuting excuses from US Transportation Secretary Pete Buttigieg that the Key Bridge “was simply not made to withstand a direct impact on a critical support pier from a vessel that weighs about 200 million pounds,” Bell responded, “Why wasn’t there a retrofit for the Key Bridge? Especially when you see that the nearby Delaware Memorial Bridge is undergoing a vessel collision protection upgrade right now?

“There should have been planning for this, given the size of vessels that were going by,” she added.

Donald Dusenberry, a “longtime forensic structural engineer” also interviewed by Reuters, questioned the lackluster barriers around the main members that held up the bridge.

“It looks like there was some cushioning in the form of wooden or some other kind of barrier, but it pretty much looks like it was attached to the pile cap at the bottom of the piers,” he said. “And that doesn’t absorb much energy.”