Low-flying helicopters will be zipping over the Boston area in the coming days. Here’s why

If you live or work in the Boston area, you’ll likely notice low-flying helicopters zipping through the sky over the next few days.

Bay Staters who do spot the twin-engine Bell 412 helicopters shouldn’t be alarmed by the unusual sight, according to the U.S. Department of Energy’s National Nuclear Security Administration.

NNSA says it will be conducting low-altitude helicopter flights over downtown Boston and the Boston Marathon race route starting Friday and lasting through Monday to measure background radiation as part of standard preparations to protect public health and safety on the day of an event.

The NNSA choppers, which are equipped with radiation-sensing technology, will fly in a grid pattern over the areas at 150 feet above the ground at a speed of about 80 mph, officials said.

Flyovers will occur only during daylight hours and are estimated to take about two hours to complete per area.

In a statement, the NNSA said, “These surveys are a normal part of security and emergency preparedness activities. NNSA is making the public aware of the upcoming flights so citizens who see the low-flying aircraft are not alarmed.”

The 127th running of the Boston Marathon is slated to take place on Patriots’ Day.

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