Minimizing Coronavirus Transmission through Hospital Mechanical and Plumbing Systems
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The Centers for Disease Control and Prevention (CDC) recommends placing a patient who has an infectious disease, such as coronavirus (COVID-19), in an airborne infection isolation (AII) room. An AII room is provided with a minimum of 12 air changes per hour, all of which are exhausted directly to outside. The room is also kept at a negative pressure, meaning that the corridor air is pulled into the room and then exhausted, further protecting the safety of others in the hospital. The CDC recommends the most serious patients, ones that may undertake aerosol-generating procedures, should be the highest priority for admission to AII rooms. Lesser risk cases are at this time allowed to be in private rooms with a door closed and private bathroom (if possible), when AII rooms are not available. Hospital Emergency Room waiting areas, which could have undiagnosed patients, are exhausted directly to outside, minimizing the amount of potentially infectious viruses in the air. (Information about the virus from the CDC is being modified daily. Click here for the most recent information.)
Most of the air in a hospital is conditioned and recirculated and relies on dilution (high air change rates) and filtration for protection. All hospital air handling units are equipped with a final filter with a Minimum Efficiency Reporting Value (MERV) rating of at least MERV 14, which can remove 75 percent of particles 0.3 to 1.0 micron in size, and 95 percent of larger particles. Some hospitals choose to use HEPA filters as the final filters, which remove more than 99.9 percent of these particles.
Facility managers have asked about the ability of HEPA filters to trap the coronavirus (COVID-19). The coronavirus itself is between 0.06 and 0.14 microns in size. However, a virus does not move around “naked.” Viruses are expelled through droplets of saliva that present themselves as larger particles when they encounter a filter. Based on this information and the CDC recommendations, HEPA filtration can help prevent the spread of the coronavirus.
To successfully use HEPA filtration in an HVAC system, the HEPA filters need to be designed into the HVAC system and air handling unit. Specifically, the filters must be tightly fitted into a specifically designed filter rack with bag in/out capabilities and a blade gel seal type housing. The air handling unit fans need to have enough power to overcome the higher air pressure drop of HEPA filters. A combination of HEPA filtration, supplemented with ultraviolet (UV) lights, has a better chance of stopping the virus.
Other HVAC Measures
Hospitals can also switch to providing 100 percent outside air, and instead of “returning” the air and recirculating it through the air handling unit, “relieve” the air to outside. Most hospital air handling units, however, are only capable of providing the heating/cooling necessary to keep hospital spaces at comfortable conditions while using 100 percent outside air when the outside air conditions are between 55 degrees F and 75 degrees F. This approach uses significantly more energy than a recirculating air system. Also, the location of the outside air intake in relationship to the relief air is important, since it is important to not re-introduce the potentially contaminated air to any air intake, since the coronavirus has been reported to be capable of transmission for up to four hours on copper, up to 24 hours on cardboard, and up to two to three days on plastic and stainless steel.
Maintaining the hospital’s environment at a relative humidity level between 40 and 60 percent has been documented to decrease the survivability of viruses. Especially in winter, many hospitals in northern climates maintain lower relative humidity levels (around 30 percent relative humidity), within ASHRAE 170, Ventilation of Healthcare Facilities, standards, but lower than the 40 percent goal. A practical response by a hospital during the current coronavirus pandemic could be to increase relative humidity levels to maintain a minimum 40 percent relative humidity. The ability to maintain a minimum 40 percent relative humidity level depends on the capacity of the humidifiers and the ability of the exterior construction to keep condensation from occurring at the higher relative humidity levels and the capacity of the humidifiers.
Facility managers have also inquired about best practices for plumbing systems. Studies conducted by the World Health Organization (WHO) have shown that there is a possibility for contamination through floor drains or like fixtures. In their study, this contamination is due to the trap of the fixture being depleted through air pressure changes in the piping.
In the United States, there are strict codes regulating the venting of sanitary waste system preventing this depletion due to pressure changes. However, drains that do not see regular use do have the potential to lose the trap seal due to evaporation. Most often when a drain loses its seal the smell of sewer gas will be prominent and unlikely left unnoticed for long periods of time.
A simple preventive maintenance measure to protect against this evaporation is to dump one gallon of water down the drain to ensure that the trap is properly sealed and the potential for contamination through wastewater is mitigated. For drains in areas that do not see regular water use and are located in conditioned spaces (i.e. dehumidification, heating, etc.) it is likely that drains will require attention on a quarterly basis. For drains that see some use, such as a shower or condensate waste, this maintenance can be extended to twice a year or in some cases annually.
Additionally, keeping domestic hot water recirculation systems balanced and flowing will help ensure that sinks designated for handwashing receive adequate hot water to better support proper handwashing procedures. It is important to avoid increasing the temperature of the hot water as this may present the possibility for scalding.
Jeff Harris, PE, LEEP AP, is director of engineering for HGA. Click here for a practical guide for temporary measures, co-written by HGA’s infection control partner, Andrew Streifel, hospital environment specialist with the Department of Environmental Health & Safety at the University of Minnesota.