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Statement: “The sensors, I’m happy to report, probably were lower during the fire than they were when the I-15 was open,” Sheriff Bill Gore said Dec. 9 about burning the so-called “bomb house” near Escondido that contained dangerous chemicals.

Determination: True

Analysis: The plume of black smoke gushing from an Escondido home on Dec. 9 ascended in stark contrast to the morning’s blue sky. News media and police helicopters circled the plume as its only company.

But hundreds of feet below, at 40 different locations, bustling county officials studied how the smoke affected the air, monitoring for unhealthy levels of soot, carbon monoxide and carcinogens like benzene.

Three weeks earlier, law enforcement authorities discovered a vast collection of explosive chemicals at the house. They determined some were too dangerous to remove and dispose, so they instead decided it was safer to burn the house and incinerate the chemicals in the process.

As a precaution, authorities completely closed a section of Interstate 15, evacuated nearby homes and set the home on fire. After an hour, only its frame and chimney remained. After three hours, the interstate reopened. After six hours, Gore called the operation a success.

Addressing concerns about pollution caused by the blaze, Gore said, “The sensors, I’m happy to report, probably were lower during the fire than they were when the I-15 was open.”

Gore’s comparison is sound, according to reports released last week detailing what those sensors showed. The air near the burning house compared similarly to other parts of the county on the same day. Pollutants didn’t exceed normal levels. Measured against markers used by federal regulators, the air quality ranged between good and moderate. The difference from other days wasn’t very drastic.

The graphic to the right, for example, shows smog levels measured over two 24-hours periods: the day before the burning and the day of the burning. Smog — an unhealthy mix of pollutants worsened by sunlight and heat — peaked around noon both days but was lower on the day of the burning.

Whether the lower smog was attributable to the interstate’s closure is unclear.

More than varying levels of traffic, weather conditions often determine how much pollution is in the air. Smog typically peaks around noon each day when sunlight and temperatures are at their highest. On Dec. 9, authorities also noted a strong vertical updraft, which lifted the smoke away from the ground.

Bob Kard, who as head of the county Air Pollution Control District oversaw the monitoring, said he didn’t know whether the closed interstate directly caused the lower levels of smog, but that it likely contributed to the decline along with the favorable weather conditions.

Regardless of what role the interstate ultimately played, we’ve called Gore’s statement True because the timing of the interstate’s closure coincided with measurably lower levels of smog.

If you disagree with our determination or analysis, please express your thoughts in the comments section of this blog post. Explain your reasoning.

What claim should we Fact Check next? Please contact Keegan Kyle directly at keegan.kyle@voiceofsandiego.org or 619.550.5668 and follow him on Twitter: twitter.com/keegankyle.

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