IOWA CITY, Iowa (AP) — A series of infrastructure failures in a crumbling state dormitory caused a toxic gas leak at an Iowa police academy that sickened dozens of recruits and could have killed some of them, a workplace safety investigation concluded. At least three recruits were poisoned by potentially lethal levels of carbon monoxide after an air handling unit and a heating boiler simultaneously malfunctioned on Nov. 15 inside a three-story residence hall at the Iowa Law Enforcement Academy in Johnston, according to records obtained by The Associated Press through an open records request. One officer suffered exposure levels that were more than eight times the amount deemed unsafe.

As dozens of recruits slept, ventilation system failures caused carbon monoxide fumes released by the boiler to build up and spread through large holes in an exhaust pipe. The 48-year-old building did not have carbon monoxide detectors and, even before the incident, had been scheduled to be demolished this June. The Iowa Occupational Safety and Health Administration cited the academy in February for exposing 77 recruits to unsafe levels of carbon monoxide and for not having an effective ventilation system, records show. The agency determined the violations were serious, noting they could have resulted in disability and death, and proposed a $9,700 penalty.

The agencies reached a settlement last month in which the academy fixed the ventilation system and paid a $5,500 fine but did not admit to wrongdoing. Iowa OSHA Administrator Luther Peddy said its safety rules do not require buildings to have carbon monoxide alarms and that the settlement eliminated the hazard. Carbon monoxide is an odorless, colorless gas found in fumes produced by heating sources. It kills at least 430 people in the U.S. each year, according to the Centers for Disease Control and Prevention.

Iowa is facing requests to reimburse medical costs related to hospital visits of four poisoned officers from West Des Moines and Iowa City. Additional claims are expected that could run into the tens of thousands of dollars. In all, 86 cadets were taken by bus to six different Des Moines area hospitals for evaluation, OSHA records show. Most were showing symptoms of carbon monoxide poisoning, including headaches, dizziness and nausea.

The problems started two days before the emergency, when a coiler on an air handler unit on the roof of the building froze and broke. The unit was responsible for pulling outside air into the building and its failure contributed to a lack of fresh air inside, the investigation found. Meanwhile, two 9-inch (23-centimeter) holes in an exhaust pipe next to the boiler on the first-floor caused fumes to escape and spread. The boiler, which was shut off after the emergency, produced unsafe levels of gas when it was turned on in a test the next day. The building was closed and classes resumed elsewhere. Academy director Judy Bradshaw recently told the council that oversees her agency that the new building will have carbon monoxide detectors.