The federal agency that monitors workplace dangers has launched investigations into four Boston-area psychiatric hospitals owned by the largest private provider of mental health care services in the U.S., The Eye has learned. The hospitals facing new scrutiny by the Occupational Safety and Health Administration are run by Arbour Health System, which has been under fire by state and federal regulators in recent months for patient-care violations and concerns over the safety of workers faced with violent patients.

The four targeted hospitals are in Brookline, Attleboro, Lowell and Pembroke, according to OSHA online reports. Arbour is owned by Universal Health Services, a publicly-traded company based in King of Prussia, Pennsylvania.

OSHA spokesman Edmund Fitzgerald said he couldn’t specify the nature of the complaints from hospital workers that prompted the investigations. The probes by OSHA come on the heels of increased oversight of Arbour-owned hospitals by numerous regulators, including the Massachusetts Department of Mental Health, which licenses the hospital, the Centers for Medicare and Medicaid Services and the U.S. Department of Justice.

A year ago OSHA flagged the high number of workers assaulted by violent patients in a “hazard alert” letter issued to Pembroke Hospital that called for improved staffing and safety measures. Phillip Kassel, the lead attorney at Mental Health Legal Advisors Committee, which represents patients, said the OSHA moves were welcome because a high incidence of violence often indicates that a psychiatric hospital is understaffed or needs to provide more staff training.

Judy Merel, the director of business development at Arbour Health System, said the hospitals train their staff annually in managing  aggressive patients.  “The safety and health of our employees and patients is our greatest priority,” Merel said in an email. OSHA opened an earlier investigation into Pembroke Hospital after a 22-year-old patient attacked a nurse and nearly tore off her ear when she was trying to place him in restraints. OSHA has said it has found no violations in that probe. In August, a 35-year-old patient at Pembroke Hospital being treated for drug addiction attacked another nurse, according to a local police report.

OSHA’s hazard alert letter last year criticized Pembroke Hospital for not increasing its staffing when admitting a patient with a known history of violence. "Mental health associates are exposed to workplace violence hazards while working with acute patients. Employees have been assaulted, suffering bodily injuries while providing care to patients,” OSHA wrote in October 2015.

OSHA inspectors also noted that Pembroke Hospital had recorded 13 injuries to workers from aggressive patients in the first five months of 2015. The previous year, 24 hospital workers were injured in attacks by patients, a 41 percent increase over the injuries documented in 2013, according to the OSHA letter. Last fall, the Department of Mental Health investigated the death of a 20-year-old patient, Amber Mace, at Pembroke Hospital.

The investigator concluded that the hospital created a “dangerous and inhumane” condition in its treatment of Mace, whose body was already in a state of rigor mortis by the time any staff noticed she had died. The state inspector wrote that hospital staff had failed to conduct nighttime wellness checks on Mace. More investigations of Arbour hospitals followed, and by March, the state called on the company to correct several urgent life safety violations at four of its hospitals – in Jamaica Plain, Pembroke, Westwood and Quincy.

Problems at the four hospitals were serious enough that the state appointed an onsite monitor to make frequent inspections of the four sites and report progress to the state commissioner on mental health. Last spring, workers at Pembroke Hospital told the monitor, Lizbeth Kinkead, that they feared for their safety, according to reports and emails obtained from the Department of Mental Health.

Hospital leadership responded to the state’s report, saying that they would increase staff to allow for new patient admissions during a shift and have revamped their screening process for violent or dangerous patients. In 2007, the state issued a scathing report about mistreatment of patients at Pembroke Hospital, following a seven-month investigation into complaints from both staff and patients.

Top administrators were all replaced, including the hospital’s CEO, medical director, education director, human rights officer and crisis prevention initiative trainer. Government inspectors in 2014 cited unsafe conditions at Arbour’s 66-bed facility in Brookline and deficiencies in psychiatric treatment and evaluations for four patients there.