SPARKS, Nev.  —  Thirty-two research monkeys quarantined at a lab in Nevada were accidentally killed in May due to overheating.

Officials for the Delaware-based Charles River Laboratories confirmed the May 28 incident at its lab in Sparks for the first time in a statement issued Thursday.

The company said the death of the 32 longtail macaque in a single room of its quarantine facility there was the result of a series of human errors in the operation of the climate control. It said the incident affected no other primates and that at no point was the public ever in danger.

The company said it self-reported the incident immediately to the U.S. Department of Agriculture and the Centers for Disease Control and Prevention. The monkeys were to be used in the research of drugs.