Yale and federal officials were still searching Tuesday for the cause of Monday’s construction accident that left three injured and one dead. The construction company in charge of the site and the union representing the workers have pledged to update safety policies to prevent future accidents.

In the meantime, work has been halted on the project — a chiller plant that, when completed, will provide 20,000 tons of cool air to nearby Yale facilities at Science Park — for at least a week, University spokesman Tom Conroy said Tuesday. Meanwhile, Yale and the federal Occupational Safety and Heath Administration will conduct separate investigations into the incident, said Andy Esposito, president of the worker union Local 424 United Ironworkers, which had nine members at the site Monday.

As of Tuesday, Yale-hired and OSHA investigators were at the scene, 275 Winchester Ave., to assess the stability of the steel structure from which the beam fell. They also interviewed each worker present at the time of the incident in the hope of determining who might be responsible, Esposito said.

The only company currently under investigation by OSHA is Coxsackie, N.Y.-based Fast Trek Steel Inc., OSHA spokesman Edmund Fitzgerald said Tuesday. Fast Trek Steel is helping to complete the ironwork for the chiller plant construction, which is led by Boston-based Shawmut Design and Construction. George Colvin, president of Fast Trek Steel, did not respond to one e-mail and multiple phone requests for comment Tuesday.

Fitzgerald said that even though Monday’s incident resulted in the death of construction worker Robert Adrian, it is not prioritized over an incident that occurred at the same site last month. At that time, another worker was injured by a cherry picker that tipped over in the basement area.

“Each inspection determines its own length,” Fitzgerald said. “Injury or death may not necessarily mean a longer investigation.”

Fitzgerald said that by law, no investigation can take longer than six months. He added that investigators will check for safety violations.

Conroy declined to comment Tuesday on whether Yale could be held responsible for Monday’s incident. He also declined to comment on how the investigations would affect the construction schedule of the chiller plant.

As a result of Monday’s accident, Shawmut is considering ways to add more oversight protocols to its construction zones, CEO Thomas Goemaat told the News on Tuesday.

“Shawmut takes safety extremely seriously, as does Yale, and we are reviewing our safety procedures on our projects to increase the level of safety,” he added.

Goemaat said that to blame Monday’s accident on a lack of supervision would be “conjecture,” adding that he was not sure greater oversight would have prevented the accident. He said policies, such as the requirement for all workers to wear protective gear and the installation of guardrails and other buffers, are mandatory on all Shawmut construction sites.

“[But] in general, the more supervision, the better,” Goemaat added.

In the meantime, Adrian’s death and the injuries sustained by the three co-workers have scared others out of returning to work, Esposito said.

“They’re anxious and they’re really nervous,” he said, adding that the workers doubt it is safe to resume work.

Goemaat said there has been no communication between his company and the injured workers so far because they are currently recuperating in the hospital.

As of Tuesday afternoon, one worker remained in critical condition and another in “serious” condition at Yale-New Haven Hospital, spokesman Mark D’Antonio said. The sole injured female worker was discharged from St. Raphael’s Hospital on Chapel St. around 4 p.m. Monday, spokeswoman Liese Klein ’88 said.