It's not safe to fly; that's why it was grounded.

I don't know why everybody keeps saying the B787 is safe to fly. The FAA is not stupid. It's a big deal for the FAA to ground an entire type of plane.

A fire on a plane is a very big deal.

Imagine you're on the UA DEN-NRT 12 hour flight on a 787 and it decides that a battery starts to ignite. You can't put it out. The oxygen is consumed. The toxic fumes are filling the cabin. You can't land the thing for hours because you're in the middle of the pacific ocean. Everybody either passes out because of lack of oxygen or because of toxic fumes. The fire destroys electronics that control the plane. Everybody dies.

A fire on a plane is a very big deal, and the FAA recognizes that.