BURRILLVILLE — A security guard was removed from his assignment at Zambarano Hospital after he allegedly fired his 9 mm pistol during an encounter with a knife-wielding intruder Sunday evening.

Todd Brown, 37, of Warwick, told the police the man fled the hospital grounds after he fired a single shot at him inside a vacant building, state police Maj. Stephen O’Donnell said yesterday as authorities continued to look for the intruder.

Although investigators still had questions to answer, it appeared that Brown’s account corresponded with other reports from the scene, O’Donnell said, noting that a second security guard had heard the tussle inside the building.

The incident raised other questions about compliance with a hospital policy that prohibits weapons on the campus.

The guard’s private security company is supposed to keep its employees from carrying weapons on the Zambarano campus, said Laurie Petrone, a spokeswoman for the facility’s overseer, the Rhode Island Department of Mental Health, Retardation & Hospitals.

The North Providence company, Industrial Security and Investigators, was apprised of the policy during the bidding phase of its negotiations with MHRH, Petrone said.

The hospital informed the company and its staff of the policy a second time before the guards started working under the contract last week, Petrone said.

At the direction of the hospital’s administrator, Paul Despres, the security company was informed a third-time yesterday, said Petrone.

“We have their assurances that there will be no guns on the campus going forward,” she said.

The incident involving Brown was first reported to the state police around 8:15 p.m. Sunday.

A hospital dispatcher reported suspicious activity, including flickering lights in a vacant building on the hospital grounds, according to O’Donnell.

The dispatcher also reported that the hospital’s security personnel and the Burrillville police were aware of the situation.

About eight minutes later, the hospital telephoned again and reported that a weapon had been fired, O’Donnell said.

Brown, who was the supervisor of security personnel at the hospital, later told the police he had gone into the abandoned building and encountered a slender man who stood about 6 feet tall and wore dark jeans, a gray-hooded sweatshirt and white, dirty sneakers, O’Donnell said.

During the altercation, the man fell down a set of stairs and came back up wielding a knife, he said.

At that point, Brown fired, O’Donnell said.

The guard told the police he thought he had hit the intruder, but investigators did not find any blood or other evidence of such an injury, O’Donnell said.

Investigators did not recover the rusty knife described by Brown, he said.

The intruder fled toward Route 100 after the encounter. Also, the hospital had telephoned the police earlier on Sunday to report the presence of a vagrant on the property.

O’Donnell described the state police investigation as a standard response to any incident involving a gunshot under such circumstances.

“Any time anybody fires a firearm we’re going to inquire as to what happened and why,” he said.

A person can fire a gun justifiably to protect him or herself from an “imminent threat” of severe bodily harm or death or to protect another person from the same threat, O’Donnell said.

An attacker armed with a knife represents such a threat, he said.

Brown was the only security guard carrying a weapon Sunday night, O’Donnell said, adding that the company allows its supervisors to carry weapons.

Brown has a permit for his gun and has met the qualifications necessary for carrying a pistol as a security guard.

No patients and employees at the hospital were hurt and the hospital was operating under its regular visiting hours yesterday.

Petrone did not identify the guard by name, but she confirmed that he would not work on either of the Eleanor Slater Hospital’s two campuses in Burrillville and Cranston as the state police finish their investigation.

mreynold@projo.com