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Operating Room Over-Humidification at an Ontario Hospital

Mechanical / HVAC Healthcare Facility Expert Testimony 2022 ONSC 5061

Diact's Paul Okrutny, P.Eng, served as the plaintiff hospital's forensic engineering expert in Orillia Soldiers' Memorial Hospital v. PCL Constructors Canada Inc., 2022 ONSC 5061, a Superior Court of Justice trial concerning damage to hospital operating rooms. The facts below are drawn from the Court's public reasons for judgment.

The Loss

During a period of extreme cold, an air handling unit (AHU-104) serving the hospital's operating rooms repeatedly tripped its freezestat — a low-limit thermostat that shuts the unit down to prevent unheated outdoor air from being drawn into the building. Each manual restart caused the valve to jump to 100% open and released a chemical odour from the humidifier into the duct system. To mitigate this odour, hospital operators used the Building Automation System (BAS) to set the humidifier steam valve to a partially open position, hoping to limit how far it would open upon a restart.

In the early hours of February 12, 2008, the freezestat tripped again. The supply fan shut down — but the humidifier steam valve remained open. With no airflow, steam accumulated in the ductwork, and air at approximately 99% relative humidity, measured near 60°C, flowed unabated into the operating rooms for more than three hours. The event damaged surgical equipment and sterile supplies throughout the OR suite.

The Investigation

The sequence of events had to be reconstructed from the hospital's Building Automation System, which had logged thousands of sensor readings, valve positions, and operator commands across the days surrounding the loss. Paul downloaded the raw BAS trend data and wrote custom code to parse and correlate it — aligning temperature, humidity, fan status, and valve-position records on a common timeline. Piecing these records together, he was able to trace exactly how the system had behaved: when the freezestat tripped, when the supply fan stopped, and how the humidifier valve responded. It was this reconstruction that revealed the humidifier had kept running after the fan shut down — pointing not to operator error, but to a missing interlock: an installation issue.

The Technical Question

The central dispute was whether the humidifier should have shut down when the freezestat tripped the supply fan — even with the valve in a manually set position.

Paul's evidence was grounded in CSA-Z317.2, the Canadian standard for HVAC systems in health care facilities:

A key point of Paul's analysis: interlock sensors are basic on/off devices. They cannot detect whether the humidifier valve is modulating automatically or has been set manually through the BAS. A correctly installed interlock therefore shuts the humidifier down on any supply-fan stoppage — including a freezestat trip — regardless of the valve's control mode. The distinction between "automatic" and "manual" operation, on which the defence rested, is not one the required hardware can draw.

Findings and Outcome

The Court agreed with Paul's evidence, finding that the absence of the required interlock was an installation deficiency contrary to the contract specifications and the applicable building code — and that the hospital's manual valve setting was not the cause of the loss: had the interlock been installed, the loss would not have occurred. The hospital was awarded its full claimed damages of $908,345.13 plus contractual interest and costs.

Source: Orillia Soldiers' Memorial Hospital v. PCL, 2022 ONSC 5061 (CanLII), Pollak J., September 16, 2022. Expert: Paul Okrutny, M.Sc, P.Eng.