The house had been abandoned after the owner defaulted on a $240,000 home loan from GreenPoint Mortgage Funding, a Novato, California lender that shut down in August, 2007. The fire was one of four suspicious blazes in foreclosed properties that month in the southern Massachusetts city. All are under investigation.

The biggest surge of mortgage defaults in seven decades coincides with an increase in blazes in foreclosed properties led by states with the most repossessed homes, according to fire safety officials in Nevada, Massachusetts and Ohio.

"The more empty houses we have, the more fires we are going to see," said James Wright, Chief of the Nevada State Fire Marshal Division in Carson City, the state's capital. "It's particularly dangerous for firefighters, because they don't know what condition these buildings are in or what they might find in them."

National arson statistics for 2007, due in September or October, probably will show a significant increase as foreclosures climbed toward an all-time high in 2008's first-quarter, said James Quiggle, a spokesman for the Coalition Against Insurance Fraud in Washington.

"Home arsons follow foreclosure trends, with a lag," Quiggle said, pointing to an increase after the last housing slump when the number of blazes reached 116,600 in 1992 from 111,900 in 1990. "We're facing a potential spike in arson like we have never seen before."

The most recent national data is from 2006, when the median price of a US home reached an all-time high of $221,900, as measured by the National Association of Realtors. There were 31,000 arsons that year, compared with 31,500 in 2005, according to the US Fire Administration in Emmitsburg, Maryland.

Profit usually is not the motive when foreclosed properties burn, Quiggle said. Cases such as Sheryl Christman, 38, sentenced in February to five years probation for torching her Caledonia, Michigan, home four days before it was repossessed are the "exception not the rule," Quiggle said.

Insurance pays the replacement cost, which rarely covers the mortgage of a property in foreclosure, he said. The value of the land is not covered.

"It takes a lot of chutzpah to set fire to a house when you're the policy holder and would be first on any suspect list," Quiggle said. "It doesn't take much for a squatter to knock over a candle or for some kids to set a fire when a building is vacant."

Last year, fires in vacant Nevada buildings increased 4 per cent from a year earlier, said Wright, the fire marshal. That number may grow, he said. The state had the worst foreclosure rate in the US during the first quarter, with one filing for every 54 households, according to data compiled by RealtyTrac Inc The national rate was one filing per 194 households, analysts at the Irvine, California company said.

In Ohio, where one of every 161 households had a foreclosure filing during the first quarter, the number of blazes in vacant buildings rose 18 per cent in 2006, according to the latest figures compiled by the state's Division of State Fire Marshal in Reynoldsburg.

Damages climbed 52 per cent to $22.7 million from a year earlier in the state where home sales began tumbling in 2004's second half, a year before the national decline began.

The value of homes owned by US banks more than doubled to $8.6 billion in the first quarter of 2008 from $3.59 billion a year earlier as lenders repossessed homes in default, data compiled by Federal Deposit Insurance Corp in Washington show.

"Empty buildings have more fires and more serious fires than occupied buildings," said Steven Westermann, president of the International Association of Fire Chiefs in Fairfax, Virginia. "There's no one around to sound an alarm."

Nationally, there were 396,000 home fires of all types reported in 2006, the highest in 10 years, according to the latest data available from the National Fire Protection Association in Quincy, Massachusetts. They caused a record $6.83 billion of damage.

Almost two-thirds of fires that occur in unsecured vacant buildings are intentionally set, said John Hall, head of research at the National Fire Protection Association. The rate drops to 32 per cent in empty buildings protected with locks or boarded windows and 7 per cent in occupied homes, he said.