For the second day in a row, students in RSU 20 schools will be sent home early due to high temperatures and humidity levels.

Superintendent Bruce Mailloux said at 10 a.m. Thursday that high school and middle school students will be released at 11:30 a.m., and that elementary students will be dismissed approximately an hour later (the exact time will depend on when the buses arrive there).

Earlier Thursday morning, Mailloux said teachers have been doing their best to counter the effects of the heat and humidity — making sure students are getting enough water, and moving to cooler locations within a building when possible.

Mailloux said there had been a feeling among staff members earlier on Wednesday that while it was hot and uncomfortable, classes could still continue. By noontime, however, Mailloux said the conditions had become “oppressive.”

“We had classrooms yesterday where the temperature was in the 90s,” Mailloux said on Thursday. “In some places, in the upper level of a building, they were over 100. That’s just not safe.”

Mailloux said school officials wanted to err on the side of caution, which prompted the decision to send students home. As with other similar decisions — i.e., snow days — the decision to release students early applied to all schools in the nine-town district.

“When we do it for one school, it’s the same for all,” said Mailloux.

According to a heat advisory issued by the National Weather Service in Gray early Thursday morning, “Very hot temperatures and moderate to high humidity levels will combine to bring uncomfortable and potentially dangerous heat to the region again this afternoon.”

The advisory applies to a large area, covering most of southern New Hampshire and the Maine coast from Kittery to Waldo County. Both coastal and interior Waldo County are covered by the advisory, which notes this will be the fifth consecutive day of 90-degree heat in many areas.

“Temperatures in the mid- to upper 90s are possible further inland, where an afternoon sea breeze will not bring relief,” the advisory notes.

The advisory goes on to make specific mention of schools: “With many buildings and schools not having air conditioning, this long-duration heat wave will allow buildings to get very uncomfortable and dangerous for those susceptible to excessive heat.”