AN EXPLODING toilet in a Barcelona bar has seriously burnt a woman who will now undergo skin grafting on her legs.

The freak incident was caused by a build-up of methane gas in the bar toilet, which was then ignited by a spark when the woman flicked on the light switch.

The build-up is thought by police to have been caused by a lack of ventilation and a highly unclean septic tank.

As the woman was sitting down when she flicked the light, the gas was compressed and therefore caused a stronger blast.

She suffered second and third degree burns to both legs.

She is now seeking legal action against the bar, in Barcelona’s gothic quarter.