The race to build out advanced cellphone networks in the U.S. has contributed to a spike in deaths among tower workers, making this one of the industry's deadliest years and drawing fresh scrutiny from federal regulators.

At least 10 workers have died in falls from communication towers so far this year, and three more were seriously injured. That included four climbers who have fallen from U.S. cell sites so far this month, including one on Saturday.

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