Mansfield Place, an Essex-based assisted living and memory care facility, paid a $3,000 fine last fall stemming from an incident in which several employees were exposed to high levels of carbon monoxide.

The fines followed a Vermont Occupational Safety and Health Administration investigation that found the facility failed to maintain adequate ventilation and CO alarm systems in its underground parking garage, allowing several employees to come into contact with high levels of the deadly gas.

State officials say the May 2018 incident occured after an independent contractor’s street sweeper malfunctioned and emitted large volumes of CO while cleaning the garage. The gas then rose through a stairwell and elevator shaft, spilled onto the first floor and set off an alarm, documents show, forcing the facility’s staff to evacuate. The incident sent four employees to the hospital for CO exposure.

Robert Murano, president of Mansfield Housing Group, which manages Mansfield Place, said building code at the time of construction didn’t require CO2 alarms in the parking garage. And while the garage does have a ventilation system, it was “overwhelmed” by the of the “extraordinary” carbon monoxide build-up.

The first alarm triggered around 10 a.m., documents show, while several employees told emergency responders that they felt headaches come on more than an hour prior.

Exposure to high levels of carbon monoxide can cause disorientation, unconsciousness and, in some cases, death. Investigators gauged the vehicle’s emissions at nearly 500 parts per million, while emergency responders found readings of over 200 ppm in the garage and some of the facility’s nearby corridors, stairwells and an elevator shaft, state records show.

OSHA standards prohibit worker exposure of more than 35 ppm averaged during an eight-hour time period, or 200 ppm during any given time.

But two Mansfield Place employees were exposed to CO levels of at least 270 ppm, according to state records. One employee reported feeling nauseous and dizzy, with the slightest amount of physical exertion causing her to feel as if she had “ran a marathon.” Another was exposed to the gas for more than two hours.

The watchdog department categorized the violations under its most serious designation: high severity, with a “greater probability” of permanent injury or death.

The department initially handed down nearly $13,000 in fines but lowered the penalty after meeting with Mansfield Place representatives, who outlined several steps to abate the violations, including more than $13,000 toward two CO sensors and an exhaust fan in the parking garage. The facility also posted a safety sheet and will require all employees to take a hazardous chemicals training course, and Murano said his organization no longer works with the independent contractor.

Murano felt the $3,000 fine was more reasonable than the initial penalty. He called the incident a “scary event” but said he’s grateful no one was seriously injured.

“I believe we’ve improved everything and took measures that it will not happen again,” he said.

Editor’s note: This story was updated to correct several references of CO2, the abbreviation for carbon dioxide, to CO, the abbreviation for carbon monoxide. We regret the error.