Codes, Comfort, and Care: Strategies for Operating Room Climate Control

May 27, 2014  |  Steve Grosjean, Controls Engineer

Like so many issues in healthcare infrastructure design, requirements for operating room humidity have undergone significant changes.

This state of change can create confusion around questions of compliance with codes, as well as how to deliver an environment that is best-suited to the needs of patients and caregivers.

Changing requirements

In the past, the guideline minimum for operating room humidity was 35% Relative Humidity (RH). Recent changes in ASHRAE 170 – Ventilation of Healthcare Facilities have lowered the minimum humidity guideline in an operating room to 20%. The standard range for ORs is now 20% to 60%.

The previous minimum requirement of 35% RH made it inefficient to manage the operating room humidification at the facility’s air handling unit, so point-of-use humidifiers were frequently used. Typically, it did not make sense to raise the entire facility’s relative humidity to maintain the humidity requirement for the ORs. With the reduction of minimum humidity to 20%, it is now economical in many facilities to control OR humidification at the air handling unit.

Point-of-use humidifiers may still be useful for a facility. They allow for a higher degree of responsiveness and localized control in a given room. For facilities seeking to meet a higher minimum humidity, or facilities running at higher temperatures, point-of-use humidifiers help to achieve desired conditions without the need to over-humidify the entire facility. The trade-off, however, is that point-of-use humidifiers require more maintenance and are sometimes placed in hard to access locations.

The right capabilities

As for operating room temperature, consistency is key. Whatever the desired or necessary temperature, it is important in the OR environment to maintain it within a degree above or below the target.

Depending on the procedure being performed in the operating rooms and upon surgeon preferences, some ORs will require a temperature range that is outside of that which is specified in the codes. At Fosdick & Hilmer, we design our operating room HVAC systems to respond quickly to thermostat adjustments in order to ensure that the environment is optimized for each procedure.

In order to achieve rapid response to set-point changes and maintain the optimum environment, it is important to place temperature and humidity sensors close to the patient’s location, so that they sense the same temperature and humidity that the patient and staff are sensing, minimizing the system delay in responding to the change.

Temperature and humidity

It’s important to consider how temperature and humidity will work together, too. For example, if specific procedures require a lower than normal room temperature, there may be a need for dehumidification in order to stay within the room humidity guidelines. Likewise, if procedures require a higher than normal room temperature, the room may require more humidification than the other rooms, and a point-of-use humidifier may be required. If possible, specific rooms should be designated for such procedures in order to minimize the number of point-of-use humidifiers. If a point-of-use humidifier is used, it is important to install it where there is sufficient duct length on the discharge side to enable the humidity to be absorbed into the airstream. If the steam is not fully absorbed in the airstream before it contacts the air devices, water droplets can collect on the diffusers and a fog – that could be mistaken as smoke – can discharge into the room.

Operating room HVAC and temperature control design require careful planning among surgeons, staff, architect and engineer; and the design engineer should have experience in avoiding the many pitfalls that can produce sub-optimal performance.






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  1. WilliamMek says:

    I really liked your article.Really thank you!

    May 12, 2016