Chrysler's response to a recall of about 1.6 million Jeep Liberty and Grand Cherokee models over rear-impact fire hazards depends on the protection a trailer hitch would provide for the gas tank. But tow hitches were not designed to protect the gas tank, according to the executive who was in charge of engineering when Jeeps like the Grand Cherokee were designed.
In addition, safety groups say that before letting Chrysler use such an unusual remedy, crash tests should be commissioned by the National Highway Traffic Safety Administration -- which has no safety standard detailing the construction and strength of trailer hitches, part of what automakers typically call a tow package.
"The tow package does not protect the tank," François J. Castaing, Chrysler's vice president for engineering in 1988-96, said in a 2011 deposition. "The skid plate underneath only protects the tank from stones from the ground."
Mr. Castaing, who retired from Chrysler in 1998, made those remarks in a deposition that was part of a 2008 wrongful death suit against Chrysler filed in the Superior Court of New Jersey in Morris County by Thomas Kline, a New Jersey man. Mr. Kline's wife, Susan, died when her 1996 Grand Cherokee was struck from behind and caught fire in February 2007.
A Chrysler spokesman, Eric Maynes, declined to discuss the deposition. Mr. Castaing did not return repeated phone calls.
Though Chrysler has agreed to a recall of some models, its position, explained in a filing with N.H.T.S.A., is that the Jeeps are safe and that the fatalities occurred in such severe crashes that no S.U.V. of that era would have done better.
The safety agency disagrees and has said it believes the vehicles "contain defects related to motor vehicle safety." The agency says it is aware of 51 deaths in rear-impact crashes that resulted in fires.
The Center for Auto Safety, whose 2009 request to N.H.T.S.A. to investigate the fire issue led to the recall, said its research found 161 deaths in 115 crashes that involved fires resulting from rear-impact collisions or rollovers. The center says a fuel-filler hose on the Grand Cherokee is also prone to pulling loose, something the safety agency did not investigate.
N.H.T.S.A. asked for a recall of 1993-2004 Grand Cherokees and 2002-7 Liberty models last month. After first refusing, Chrysler persuaded the agency to accept a compromise: it would recall 1.6 million 1993-98 Jeep Grand Cherokee models and 2002-7 Jeep Liberty models and install trailer hitches.
Chrysler said it would conduct a service campaign instead of a recall on the 1.1 million 1999-2004 Grand Cherokees and inspect nonfactory trailer hitches for sharp edges, replacing them if necessary. But nothing would be done for those models with a factory hitch or no hitch.
Officials from the safety agency were not available for an interview because the investigation has not been completed, a spokeswoman, Karen Aldana, wrote in an e-mail.
Asked how agency officials could initially demand that the 1999-2004 Grand Cherokees be recalled and then decide a few weeks later that a recall was not needed, the agency issued a statement saying it had concluded there was "a lower rate of post-crash fires" in newer models. But it declined to provide the basis for its reversal.
Using a trailer hitch to reduce a rear impact is an unusual concept, said Pam O'Toole Trusdale, executive director of the National Association of Trailer Manufacturers. "It is not something we would have ever considered," she said in an interview.
But in a statement, N.H.T.S.A. said, "We believe the risk presented by all vehicles involved is being adequately addressed." The agency declined to provide the basis for that conclusion.
Even Chrysler said there were limits to what a trailer hitch can do. In a report to the safety agency, Chrysler said the hitch "cannot and will not mitigate the risk of high-energy rear collisions" and it would "incrementally improve the performance" in "certain types of low-speed impacts."
But it is the high-speed crashes that cause fire fatalities, Clarence Ditlow, executive director of the Center for Auto Safety, said.
The trailer-hitch solution might help, Adrian Lund, president of the Insurance Institute for Highway Safety, said.
"It certainly could if it is mounted strongly -- then it is like a lower bumper, almost," he said in an interview. But, Mr. Lund said, N.H.T.S.A. should test it.
Earlier this month, the Center for Auto Safety asked for the hitches to be crash-tested.
Ms. Aldana declined to say whether the safety agency had approved the hitch or decided whether to conduct crash tests. Instead she provided this e-mail statement: "N.H.T.S.A.'s investigation remains open pending completion of the agency's review of the remedy announced by Chrysler. As part of its review, the agency will determine whether additional action is warranted."
Mr. Lund said that a test by the insurance group showed it was possible for the front of a passenger car to dive below the rear bumper of a Jeep, which, for ground clearance when driving off-road rides higher than a passenger car.
That test, conducted in 2004, was to see how well the rear bumper of a 2004 Grand Cherokee held up to an impact. The Jeep was struck by a 2004 Dodge Stratus sedan at 10 miles per hour and, while the gas tank was not damaged, the adjacent heat shield was damaged.
Trailer hitches are not a remedy because they can puncture the gas tank in a crash, Mr. Ditlow said, noting the death of 4-year-old Cassidy Jarmon in a 2006 fire in Cleburne, Tex.
A police officer investigating the accident told The New York Times that she concluded that the hitch on the 1993 Grand Cherokee punctured the gas tank, leading to the fire. The girl, who was strapped into her child seat, survived the impact but died of injuries from the fire.
For Jeep owners who want fire-extinguishing potential, a Scottsdale, Ariz., company says it will be offering a Jeep version of its Fire Panel.
That is a one-inch-thick plastic panel that fits over the gas tank. When struck, it shatters, spraying a powder to extinguish a fire, said W. David Hoffman, the business development manager at Firetrace International. Mr. Hoffman said the price had not been set and would depend on volume.
Mr. Hoffman said that about 50,000 Fire Panels had been sold to police departments concerned about fire hazards in their Ford Crown Victorias, which also have gas tanks behind the rear axle.
In 2005 the Army's Research Laboratory tested the panel on military vehicles to see if it would protect fuel tanks from "ballistic threats." It concluded that the panels worked so well that "crew members should not be subjected to hazardous fires." The panels are used by the military, said Joyce P. Brayboy, a spokeswoman for the Army Research Laboratory.
Correction: July 13, 2013, Saturday
This article has been revised to reflect the following correction: An earlier version of this article cited an incorrect date for the deposition given by François J. Castaing a former vice president for engineering at Chrysler. It was 2011, not 2001.
This article originally appeared in The New York Times.