Millions of owners of vehicles equipped with Takata air bags may have to get repairs done more than once, because of shortages of replacement parts and uncertainty over whether repair parts already installed are defective, auto industry officials and safety regulators said on Tuesday (2 June).

A House subcommittee held a hearing as part of an investigation of problems with Takata air bags that have been linked to six deaths and one of the largest consumer product recalls in US history.

Lawmakers probed as to when owners of affected vehicles, which could number as many as 34 million in the US, can be sure that their air bags are safe.

Just so people are clear to cut through any of the talk surrounding us – are the replacement devices safe? Texas Congressman Michael Burgess asked. Not safer but safe, unequivocally safe?

People need to look up their VIN number (Vehicle Identification Number) now, and if they have a recall to go get a replacement inflator, they need to do that, said Mark Rosekind, head of the National Highway Traffic Safety Administration (NHTSA).

In a written testimony ahead of the hearing he said a replacement part may not be immediately available due to the scope of the recall.

What we will do is identify if there is an interim remedy, because some of these may not have the longevity needed to make sure that its a lifelong – for the entire life of the vehicle – fix, Rosekind told the hearing.

Carmakers are concerned that a lack of available replacement parts might cause many consumers to ignore the recall. The problem has taken on increasing urgency this year as Takata has continued to expand the list of potentially defective air bags.

The inflators in those air bags are prone to rupture and send shrapnel into vehicle occupants. They have been linked to hundreds of injuries, according to NHTSA.

Ten passenger-car manufacturers since 2008 have announced recalls involving ruptured inflators in Takata air bags, and their dealers have been replacing the affected parts as they have become available from the company and, more recently, other suppliers.

Takata last month said certain air bags that already have been repaired may need to have parts replaced a second time.

Another complication is that the recall involves both driver- and passenger-side air bags. Neither Takata nor NHTSA can say how many vehicles in total may be affected or how much overlap there may be.

The House subcommittee on commerce, manufacturing and trade also heard testimony from Takata executive Kevin Kennedy and representatives of two vehicle manufacturer trade groups.