BOISE, Idaho (AP) — Crews who battle wildfires will have to wait at least another year before getting better fire shelters than those that failed to save 19 firefighters trapped by flames in Arizona four years ago.

The U.S. Forest Service told The Associated Press on Thursday that the deaths sped up work to get an upgraded shelter in place this year, but the effort has been pushed back a year after prototypes couldn't outperform the shelter developed in 2002.

That 4.5-pound (2-kilogram) shelter can withstand direct flames and 2,000 degrees (1,090 Celsius) for about a minute.

The Forest Service says it could save lives if it can create a shelter of equal weight to withstand those conditions for two minutes.

The agency says it won't meet a December deadline despite help from NASA, research universities and private companies.