I got a little queasy reading this. Quite thankful the explosion did not occur in the FA. 
From FlightGlobal:
A stewardess caused £20,000 of damage on a Boeing 747 flight from Heathrow to Miami, after she heated up a ready meal she had bought from a supermarket.
The curry blew up in the high-powered microwave, which was in the club class kitchen.
Staff had to use a fire extinguisher to control the blazing oven, although BA insists there was no threat to passengers' safety. However, the 747 needed days of repairs.
The airline sent a warning email to its staff, explaining that onboard food needs special packaging because its club class microwaves are twice as powerful as domestic ones.
A BA employee said, "Many cabin crew like to bring their own meals to eat.
"At first we thought the microwaves were a godsend. But this unfortunate incident has left us with egg on our faces."
BA stressed, "At no time was there any danger to passengers or the aircraft."