A GRANDMOTHER was forced out of her home after vandals sprayed a harmful fire extinguisher through her letterbox.

Ms Patricia O'Mahony spent Friday night at a neighbour's house after the first floor of her home in Thamesdale, London Colney filled up with an intoxicating powder which if inhaled in large doses could be fatal.

The 64-year-old had to employ a firm of industrial cleaners to clear up the mess before she was allowed back into the property. She now plans to lock up her letterbox at night in fear of further attacks.

Speaking after the ordeal she said: "They are not fussy about what they put through it and next time it could be a firework or anything. It's a shame, but you have to safeguard your own home."

The dry powder extinguisher is normally used to put out electrical fires. It contains significant amounts of sodium bicarbonate. St Albans firefighter Trevor Ray said the substance could be potentially fatal if breathed in, in sufficient quantities.

He added: "People might just think it was a prank, but it was a very dangerous thing to do."

Ms O'Mahony was watching TV alone at around 8.45pm when she heard a noise at her front door. As she got up out of her seat to investigate she heard the smoke alarm go off.

She said: "There was this cloud of smoke bellowing through and I thought it was a fire. I tried to go through the kitchen, but that was filling up with smoke too.

"I was coughing a bit, but managed to make my way to the front door and just saw this 2ft high extinguisher outside with the nozzle sticking through the letterbox.

"I just pulled it out and rang 999.

"It happened so quickly and it is amazing how much came into the house in such a short period of time. It was like someone emptied a sack of talcum powder and threw it about the house."

Police, ambulance and fire crews all arrived at the scene and Mrs O'Mahony was given an oxygen mask to help her breathe. Fire crews used fans to clear the powder and advised the pensioner to spend the night at her neighbour's to avoid inhaling the dust.

Returning to her house the next day, Mrs O'Mahony was faced by a "blanket of white powder which just covered everything".

She added: "It was just too much for one person to clean up. The powder gets into everything and the whole place had to be cleaned from top to bottom."

It is believed the extinguisher may have been stolen from a garage forecourt. The vandals failed in an earlier attempt to set it off in a block of residential flats nearby. Police are appealing for any witnessess to contact them on 01707 638102 .