EAST DEER — About 200 township residents evacuated Monday when a derailed tanker leaked a toxic gas into the Allegheny River might not be allowed to return to their homes until sometime Wednesday.

Anhydrous hydrogen fluoride gas leaking from the derailed, overturned and submerged tanker can, if released into the air, cause eye, nose and throat irritation and fatal lung damage, according to the federal Agency for Toxic Substances and Disease Registry.

When mixed with water, the gas turns into hydrofluoric acid, a corrosive chemical used for industrial applications, said Don Bialosky, an emergency response coordinator with the state Department of Environmental Protection.

Bialosky described hydrofluoric acid as “one of the nastiest acids around.”

At least one water authority temporarily shut off river intakes Monday night when fluoride levels increased. The intakes were later opened.

Clean-up crews were expected to work around the clock as evacuated residents sought overnight shelter with relatives and in a New Kensington hotel.

“We’re anticipating this is going to be a long-term event, 48 hours and not 24,” Robert Full, chief Allegheny County Emergency Management coordinator, said late Monday.

The Norfolk Southern train derailed about 5:30 a.m. near the New Kensington bridge. No one was reported injured.

Of the train’s 84 cars, 13 were derailed on the tracks between Freeport Road and the Allegheny River.

Two tanker cars landed in the river. One of the cars which was almost submerged upside down, was carrying anhydrous hydrogen fluoride.

Full said three of the derailed cars carried the hydrofluoric acid, but only the one in the river was leaking. Crews were expected to bring in empty tankers early this morning to start transferring the toxic gas from the toppled tankers. It could take 10 to 12 hours to transfer the contents of each tanker, Full said.

He said officials were still weighing their options late Monday as to how to get the submerged and leaking tanker out of the water.

It’s impossible to say how much gas leaked out, Full said, but the tanker had risen about a foot in the water since Monday morning, indicating it was getting lighter.

Crews have water hoses ready in case the tanker flips over and starts to spew its contents into the air. There are about 75 people working to clear the area, Full said.

The contents of the tanker that had leaked out had moved down river about six or seven miles as of late Monday night.

Although Bialosky said there isn’t a significant effect on the river water, Oakmont Water Authority shut down its river intake for four hours Monday evening when elevated fluoride levels were detected. Water intake had been resumed by 11 p.m.

“It appears to be a slow enough leak and there are billions of gallons of water to dilute it,” Bialosky said.

Several train cars are blocking the leaking tanker. Another car is on its side in the water but isn’t leaking.

The portion of the train that didn’t derail was removed from the site about 4:30 p.m.

Mandatory evacuations were imposed on people living within a half-mile of the crash site on the East Deer side of the river, roughly from the New Kensington (Ninth Street) bridge to the 600 block of Edna Street.

The New Kensington Bridge was shut down all day. Route 28 Exit 13 was closed Monday afternoon.

All boats were barred from the river between the Tarentum and New Kensington bridges. At this time of year, that could have affected only barge traffic.

East Deer commissioners’ Chairman Anthony Taliani urged residents to monitor the news media or call the township municipal building for updates.

Taliani said Allegheny County Police would assist with overnight security in the area.

A shelter was set up at Holy Family Catholic Church at Freeport and Murrayhill roads, and the Red Cross provided housing at the Clarion Hotel in New Kensington for several families who had nowhere to go. The Salvation Army also was assisting at the scene.

The tanker cars have a 15,000 to 20,000 gallon capacity, but officials could not confirm how much of the chemical was being transported Monday.

Experts from Norfolk Southern and Texas-based Solvay Chemicals Inc., which manufactures the chemical, arrived Monday afternoon.

“The car being in the water is actually working to our advantage,” Full said. “A scrubbing effect is occurring under the water.”

He said all efforts are being made to ensure the safety of those working to get the tanker out of the water. One problem is crews are unable to get close enough to the tanker to see why the leak started and where it is.

According to the DEP’s Bialosky, anhydrous hydrogen fluoride reacts violently with water and causes it to boil, making it too dangerous for any divers to get close enough to pinpoint the leak.

Crews have been able to determine the leak is coming from near a dome on top of the tanker — which is underwater — where a hatch covers valves.

The water is rippling and bubbling near that spot, and there also is a small white vapor cloud above it, Bialosky said.

Crews plan to remove the cars in the water last to allow more mobility on land.

One concern is keeping the gas from leaking into the air once the tanker is lifted out of the water, Bialosky said.

If the gas is inhaled, the effect is instantaneous, Bialosky said. It causes the eyes and lungs to burn similar to if someone accidentally inhaled battery acid.

“It’s extremely corrosive, more so than other acids,” Bialosky said. “It will eat through glass.”

When it’s transported in its acidic form, the containers have to be lined in wax, Bialosky said.

Full said officials are working well together but he said they will be very cautious when removing the submerged tanker.

“We better be able to be prepared with what’s going to occur,” Full said. “We don’t know everything that’s going on in that tanker car.”

Officials are still investigating what caused the wreck.

Full said that while no cause has been ruled out, sabotage seemed unlikely.

“There was no communicated threat,” Full said.

It appears to be nothing other than an unusual accident, Full said.

Norfolk Southern spokesman Rudy Husband said it’s difficult to put a time frame on finding out what caused the derailment.

“With a derailment, the cause can sometimes be very obvious or it could take weeks or months,” Husband said.

He said officials interviewed the conductors and ruled out operator error.

“It’s really a process of elimination,” Husband said. “We need to look at the equipment and track, and start ruling things out,”

He said the first priority is safety and getting the tracks back together.

The train was coming from Conway and was headed for Allentown, where the cars would be put on other trains for delivery, Husband said. It was carrying a variety of products including lumber, flour, plastic pellets and corn syrup.

The tankers, which are made of double-layered steel, were bound for a factory in New Jersey, said Vance Erickson, senior vice president of Solvay Chemicals. They’re specially designed to withstand high impact, Erickson said.

“We have people on the scene that are technical experts who are assisting the emergency response people to minimize any hazard,” Erickson said. “We have people familiar with the product and the rail cars.”

“This is a dangerous chemical and we want to do the best we can to not present an unacceptable risk to the public,” Erickson said.

None of the three-member train crew was injured. They were given a routine drug and alcohol test, Husband said.

Full said late Monday all crew members were in compliance.

The FBI was on scene because it now investigates transportation accidents, Full said.

The Department of Homeland Security also was notified. The U.S. Coast Guard was called in to support emergency crews.

When asked if an apparent dip in the tracks caused the wreck, Full said that couldn’t be determined yet.

“There’s so much damage from all the cars and all the weight, we don’t know if a car carved that section out or if the bank slid,” Full said.

“There are cars on top of cars, so it’s really hard to make that determination without the right people to assess it,” Full said.

The New Kensington side of the river has not been evacuated, but Mayor Frank Link and Police Chief Chuck Korman spoke with emergency management coordinators should residents be required to leave the area.

The Alle-Kiski Medical Center rerouted patients from Citizens Ambulatory Care Center in New Kensington to Allegheny Valley Hospital in Harrison, said Kelli Serencsa, AKMC spokeswoman.

The hospital also is prepared with antidotes should anyone inhale the gas, Serencsa said.