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Sunlight shining through glass bottles caused March 2021 Stoneham fire, investigators say

Investigators say this is rarely the cause of a fire.

A fire at 24 Hersam St. in Stoneham was caused by sunlight shining through glass bottles, investigators say. Stoneham Fire Department

By Susannah Sudborough

3 minutes to read

A three-alarm fire in Stoneham that blazed in March 2021 was caused by a rare combination of sunlight, curved glass, and combustible materials, the Stoneham Fire Department said Monday.

The department said the cause of the fire was only discovered after a thorough investigation and was not what investigators initially suspected.

“I have heard from neighboring Fire Chiefs of solar magnification causing fires in their cities when residents remove screens from replacement windows, however, I haven’t heard of an upside-down beer bottle as the cause of a fire,” Stoneham Fire Chief Matthew Grafton said in a news release.

The fire at 24 Hersam St. broke out on March 6, 2021, at approximately 11:15 a.m. The Stoneham Fire Department said that the first firefighters to arrive on scene saw flames coming from a second-floor deck on the side of the four-family house, and quickly discovered that the flames had spread into the ceiling and attic.

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Stoneham fire said it needed help from a dozen other fire departments to put out the fire. By the time the fire was out, it had caused more than $700,000 in damages and two firefighters were injured.

A fire at 24 Hersam St. in Stoneham was caused by sunlight shining through glass bottles, investigators say. – Stoneham Fire Department

Once the fire was under control, investigators quickly went to work. Based on an examination of the damage, burn patterns, and witness statements, they soon focused on the second-floor deck as the point of origin, the fire department said.

With the point of origin identified, investigators found what appeared to be the obvious cause of the fire: discarded cigarette butts near trash scattered across the floor of the porch that could easily catch fire.

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“We all initially thought it was going to be the cigarettes,” Fire Captain Jim Marshall said.

Careless disposal of cigarettes and smoking accessories is a common cause of structure fires in Massachusetts, and fires on porches tend to rise in the early spring as people begin to step outside more often, Stoneham fire said.

However, investigators soon learned that no one had been on the porch in the hours before the fire, the department said. Residents reported that they hadn’t been on the second-floor porch all morning, and their statements were corroborated by footage from a neighbor’s video camera system.

Investigators soon determined that there were no electrical wires, devices, or components in the area that could have ignited a fire, Stoneham fire said.

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“We’re trained to use the scientific method and work our way through all the steps,” Stoneham Police Sgt. Dave Thistle, a member of the Stoneham Fire Investigation Unit said.

“We had a K-9 come in to make sure there were no accelerants, and we worked to rule out every possible cause we could come up with and narrowed it down to smoking or our rare solar theory.”

In addition to showing that no one had been smoking on the porch that morning, photos and video showed that the area of origin was in direct sunlight for about five hours preceding the fire, providing ample time for the sun’s rays to be focused through the glass bottles onto the combustible items nearby, Stoneham fire said.

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“We are all familiar with the concentration of sunlight by a convex lens or a concave mirror,” Jeffrey Baumgardner, senior research scientist at the Boston University Center for Space Physics said.

“Some bottles (with or without some liquid inside) could act as a lens…There are well-documented cases where large buildings with curved faces covered by glass have focused the sun on cars and have melted the plastic in the interiors.”

Of about 16,000 structure fires in Massachusetts during an average year, fewer than 10, or less than one one-thousandth of one percent, are attributed to sunlight as the heat source, State Fire Marshal Peter Ostroskey said in the release.

“It’s uncommon but definitely not unheard of,” he said. “We’ve seen several fires involving windows, mirrors, and other glass surfaces. This was the first one we can remember involving glass bottles, but there’s no question these surfaces can concentrate sunlight into a competent heat source under the right circumstances.”

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