On the 747, at least. Maybe it has addressed this in the Dreamliner.
From The Register:
Forget binary liquid explosives, a British Airways stewardess has shown how it’s really done by popping her curry ready meal into a 747’s club class microwave, with explosive results.
The spicy blast — caused by the supermarket-bought nosh’s inability to withstand the might of the double-strength airborne microwave — provoked crew on the Heathrow to Miami jaunt to deploy a fire extinguisher “to douse the blazing oven.”