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ASHRAE 170 Overview For Filtration of Hospitals

March 14, 2017 |

Operating Room Filters

ASHRAE 170 provides an outline for Hospital and Healthcare Facility Ventilaiton and Filtraiton, and is the basis for CMS, FGI, and Joint Commission standards.  This article is not a substitue for the actual standard, what will provide you with the "highlights" of ASHRAE 170 as it pertains to Healthcare/Hospital filtration.

What can not be stressed enough is that ASHRAE 170 and the regulatory agencies that inspect hospitals and healthcare faciltites have establised these requirements as minimum standards - meaning it is very common for the risk assement, infectious control, and legal teams within a hospital or other healthcare facility to go above and beyond these requirements.  Think of it this way: Whould you prefer to be treated in a "minimum standard" facility or would you prefer a level of care that takes into account your risks as a paitent more seriously?

It is painful to be in this industry and walk into and audit so many hospital and healthcare facilities that have chosen to go to the minimum standard as sufficent and put paitent care behind the inital design and operating costs.  Understandably not every facility can be state of the art, jsut as not everyone can drive a porsche, but in some cases the minimum standards present more risk to paitents than they are aware of or the people in charge of these facilities are aware (sometimes electively ignorant).  Do not interpret this as because you are exceededing these guidlines that you can than dial back your ventilation and filtration systems - which is a question we get asked often.

Supply Air:

Most air handling units in hospitals require two banks of filters, they are defined as Filter Bank #1 which is to be upstream of the heating and cooling coils, and Filter Bank #2 which is to be downstream of all coils and fans/blowers.  Filter Bank#2 must also have a "sealing interface"  For paitent care and OR areas filter bank #1 must be MERV-7 or higher and Filter Bank #2 must be MERV-14 or higher.  (That's correct - HEPA filters are not required in your OR, but it is best-practice to have ceiling mounted HEPAs for proper protection of your paitents)  Labratories and Class A Surgery need to have MERV-13 as a minimum and those can be in either filter bank.  Administrative, Storage, and even skilled nursing areas only need MERV-7 in Filter Bank #1.  Supplemental air filtraiton through in-room purifiers and Upper Air UV light systems has gotten inexpensive and with how effective these units are it is best practice to have these in place as an added layer of protection for the hospital staff.  It was also added in the 2013 revision if ASHRAE 170 that all filter banks with MERV 13 or higher must be monitored with a differential/static pressure differential monitoring device.

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Exhaust Air:

The regulations for exhaust air are specific to specific areas and do not have as general requirements that the supply air does.  For AII, Bronchoscopy, ER Waiting, nuclear medical labratory, and labratory chemical fume hoods the exhaust ductwork must maintain negeative pressure so the air does not leak into other spaces of the facility.  The discharge must also extend a minimum of 10 feet above the nearest roof, intake, doors, or noramlly accessible area within a 10 foot radius of the discharge stack.  This is to minimize the possibility of the contaminated air to re-enter the hospital.  Most of these spaces also require that the exhaust air be HEPA filtered, and some are recommended to incorperate carbon filtration.

Energy Recovery on Exhaust air is more generalized, and it is simply stated that it "shall not allow for any amount of cross contaimination" This limits the energy recovery methods available when selecting and AHU/HVAC system and also means that for AII or Combined Isolation Rooms no energy recovery is allowed.

Room Specific Requirements:

The three most common rooms that have specific air filtraion requirements above and beyond the general guidleines are Airborne Infectious Isolation (AII), Protective Environment (PE, which one could aruge that Operating Rooms rooms are PE rooms but are not currently classified that way), and Morgue/Autopsy Rooms.

  • AII:  These rooms are required to be at a minimum of -0.01" pressure to adjoing spaces, with exhaust air being HEPA filtered and not able to mix with other air streams.  The exhaust grille(s) must located either in the ceiling directly above the paitent bed or on the wall near the head of the bed.  An in-room purifier and Upper Air UV light system is also a best practice to help protect the hospital staff from airborne infections.
  • PE: Essentially the opposite of AII rooms, these must be maintained at +0.01" to adjoining spaces, the the supply air being HEPA filtered.  The supply air grilles/diffuser must also be installed in the ceiling directly above the paitend bed or in the wall above the head of the bed.  Because of the immunodeficiency of the paitents it is also advisable to treat the supply air with a carbon/molecular filtration system, and incorperate an Upper Air UV light system for further protection against airborne pathogens that may be harmful to the paitent.
  • Morgue/Autopsy: These rooms need to be maintained at a -0.01" pressure relative to adjoining spaces and needs to be exhausted directly outdoors.  Because of the chemicals used in this process and the potentially noxious smells emitted from the deceased it is recommended to have some kind of molecular/carbon filtration in a multi-pass system so these chemicals and odors do not create a problem wherever they are being exhuasted to.

Hospital air filtration and ventialation is one of the more dynamic environments for airborne pathogen and particle control, which is why we've made the ebook "Hospital Ventialation and Filtration" available free of charge.  Just click the link to download it today.







Tags: Ventilation Health Hospital FAQs

Written by Ben Klawitter