DETROIT -- Two U.S. senators are calling on regulators to issue a nationwide recall of cars with faulty air bags made by Takata Corp., questioning why automakers have been allowed to limit recalls to only certain locations with high humidity.
Democratic Sens. Richard Blumenthal of Connecticut and Edward Markey of Massachusetts made the demand in a letter to Transportation Secretary Anthony Foxx, who oversees the National Highway Traffic Safety Administration.
Air bag inflators made by Takata can rupture, causing metal fragments to fly out in a crash. Safety advocates say the problem has caused four deaths and multiple injuries. So far automakers have recalled about 12 million vehicles worldwide due to the problem.
But in the U.S., many automakers have limited their recalls to certain high-humidity areas. Takata has recommended that automakers conduct recalls only in Florida, Hawaii, Puerto Rico and the U.S. Virgin Islands - areas with high "absolute" humidity. Some automakers have included a few more states, but cars in many states with high humidity levels have been excluded.
CBS News has discovered complaints of airbags exploding in multiple states outside the recall zone, including Indiana, Ohio, Illinois, and Maryland.
No firm cause of the problem has been identified. Takata and the National Highway Traffic Safety Administration are investigating the impact of prolonged absolute humidity, which is a measure of the moisture content in the air, on chemicals that propel the air bags in a crash. They're looking into whether moisture in the air can cause the chemicals to explode with too much force, causing metal parts to fracture.
In their letter, the senators ask Foxx to encourage automakers to provide drivers with free loaner cars if parts aren't available. They're also dubious of the reasons given so far for limiting the recalls.
"Almost any area of the country may have high heat and humidity for an extended period of time, including the Northeast. The lines they've drawn are completely senseless and arbitrary," Blumenthal said in an interview. "It would be laughable except it's deadly serious in its consequences."
The senators' letter also notes that people drive their cars from the Northeast to spend weeks or months in higher-humidity southern states.
Takata air bags have been the subject of recalls for several years, but U.S. regulators didn't open an investigation into them until June. This week, NHTSA issued rare warnings to owners of nearly 8 million recalled cars equipped with the air bags to get them repaired as soon as possible.
The agency's website crashed Monday night and still isn't working fully, so drivers aren't able to plug in their vehicle identification numbers to see if their vehicle has been recalled. Deputy NHTSA Administrator David Friedman said the crash likely was caused by a software change.
The Takata-related recalls so far cover certain vehicles made by BMW, Chrysler, Ford, General Motors, Mazda, Honda, Mitsubishi, Nissan, Subaru and Toyota.
Messages were left Thursday seeking comment from Foxx and NHTSA. Takata issued a statement that did not address a nationwide recall. The company said it's supporting the NHTSA investigation and has a joint objective "to do all that is possible to maximize motor vehicle safety."
Karl Brauer, senior analyst at Kelley Blue Book's KBB.com, said that Takata is one of three global airbag manufacturers and controls over 30 percent of the international market.
"This means not only is a potential defect within their assembly process far-reaching," he told CBS MoneyWatch, "but the production logistics of replacing all those defective airbags, while also keeping up with ongoing production demand for new-car airbags, will be challenging to say the least -- 'impossible' would probably be a more accurate word."
The NHTSA released an updated advisory Tuesday night with a new list of the vehicles being recalled:
BMW: 627,615 total number of potentially affected vehicles:
2000 - 2005 3 Series Sedan 2000 - 2006 3 Series Coupe 2000 - 2005 3 Series Sports Wagon 2000 - 2006 3 Series Convertible 2001 - 2006 M3 Coupe 2001 - 2006 M3 Convertible
Chrysler: 371,309 total number of potentially affected vehicles:
2003 - 2008 Dodge Ram 1500 2005 - 2008 Dodge Ram 2500 2006 - 2008 Dodge Ram 3500 2006 - 2008 Dodge Ram 4500 2008 - Dodge Ram 5500 2005 - 2008 Dodge Durango 2005 - 2008 Dodge Dakota 2005 - 2008 Chrysler 300 2007 - 2008 Chrysler Aspen
Ford: 58,669 total number of potentially affected vehicles:
2004 - Ranger 2005 - 2006 GT 2005 - 2007 Mustang
General Motors: undetermined total number of potentially affected vehicles
2003 - 2005 Pontiac Vibe 2005 - Saab 9-2X
Honda: 5,051,364 total number of potentially affected vehicles:
2001 - 2007 Honda Accord 2001 - 2005 Honda Civic 2002 - 2006 Honda CR-V 2003 - 2011 Honda Element 2002 - 2004 Honda Odyssey 2003 - 2007 Honda Pilot 2006 - Honda Ridgeline 2003 - 2006 Acura MDX 2002 - 2003 Acura TL/CL 2005 - Acura RL
Mazda: 64,872 total number of potentially affected vehicles:
2003 - 2007 Mazda6 2006 - 2007 MazdaSpeed6 2004 - 2008 Mazda RX-8 2004 - 2005 MPV 2004 - B-Series Truck
Mitsubishi: 11,985 total number of potentially affected vehicles:
2004 - 2005 Lancer 2006 - 2007 Raider
Nissan: 694,626 total number of potentially affected vehicles:
2001 - 2003 Nissan Maxima 2001 - 2004 Nissan Pathfinder 2002 - 2004 Nissan Sentra 2001 - 2004 Infiniti I30/I35 2002 - 2003 Infiniti QX4 2003 - 2005 Infiniti FX35/FX45
Subaru: 17,516 total number of potentially affected vehicles:
2003 - 2005 Baja 2003 - 2005 Legacy 2003 - 2005 Outback 2003 - 2005 Baja 2004 - 2005 Impreza
Toyota: 877,000 total number of potentially affected vehicles:
2002 - 2005 Lexus SC 2002 - 2005 Toyota Corolla 2003 - 2005 Toyota Corolla Matrix 2002 - 2005 Toyota Sequoia 2003 - 2005 Toyota Tundra