Lower Pressure Drop HEPA Filtration?

An article in a hospital journal, suggesting that synthetic melt blown fibre filter material could be used in healthcare facilities to replace HEPA filtration, made me to do a little digging.

Every customer wants more for their money.
Every vendor wants to offer their customers more for their money.

Some companies offer what is known in the industry as synthetic HEPA filters. These filters meet the requirements of HEPA filtration (have an efficiency rating of 99.97% for removal of partials having a size of 0.3 microns) and have a lower pressure drop than true (mechanical) HEPA media. This improved performance is achieved using media that is more porous than true HEPA, with HEPA performance being achieved by applying an electrostatic charge to the media. The industry is aware that HEPA performance is achieved when the synthetic media filter is newly manufactured and also that this performance degrades as the electrostatic charge decays. Some published testing indicates that efficiency of meltblown synthetics can be reduced by as much as 30% when they are discharged and are no longer effective in the 0.3 to 1 micron range. We have carried out our own in house tests to evaluate synthetic HEPA materials and found the material as supplied achieved HEPA standards at increased airflow but when tested after a six month usage the filter had a 67% efficiency for removal of partials greater than 0.3 microns.

In today’s extremely tight economy we all endeavor to deliver better product for less cost, however, when it comes to medical grade air purification for Airborne Infection Isolation let us be ready to ask some questions regarding air filtration. Remember the CDC states that HEPA filtration at 99.97% removal efficiency, not 99.95% or 95%, is acceptable for air purification in isolation rooms.

What should we ask HEPA filter suppliers?
1)What filter media is used in your filter manufacture, pure mechanical HEPA or electrostatically enhanced synthetic?
2)If the supplier uses electrostatically enhanced synthetic media, ask for a statement of efficiency throughout filter life.

It is understood that electrically charged filter media has its application but we must be sure to understand what we are being offered and the nature of our application.

Further reading:
1) Approaches for Exposure Assessment and Control for Airborne Infectious Agents
University of Minnesota School of Public Health - Peter C. Raynor, Ph.D.
2) ANSI/ASHRAE Standard 52.2, Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size (Considers the effect of electrostatic filter discharge)
3) The Long-Term Performance of Electrically Charged Filters in a Ventilation System
Peter C. Raynor Soo Jae Chae
4) Dust loading on electrostatically charged filters in a standard test and a real HVAC system
Peter C. Raynor Soo Jae Chae

Airborne Infection Isolation Rooms (AIIR’s)

Requirements and guidelines for Health Care Airborne Infection Isolation Rooms (AIIR’s).

We are often asked by hospital staff:


“How do we produce a negative pressure isolation room”?; “We are unable to exhaust to the outside. What can we do”?


Although we can offer general guidance on the subject there are a variety of regulatory processes controlling hospitals. When trying to determine your hospitals regulatory control process it is good to start with your in house infection control personnel as there may be controls set by administration that exceed requirements of other governing bodies.


Who are these governing bodies?


Most state Health Departments have some form of documentation in place for producing AIIR’s. The documentation could be in the form of regulations or guidance and sometimes both. As a generalization the states Health Departments quote the CDC (Centers for Disease Control) “The Guideline for Isolation Precautions” which in turn references the AIA (American Institute of Architects) “Guidelines for Design and Construction of Health Care Facilities”.


How is the information obtained from these governing bodies?


• State Health Department try an internet search. Some sites are difficult to navigate so you may need to call them for information.


• CDC *HICPIC Guidelines are downloadable from their web site direct link to pdf is www.cdc.gov/hicpac/pdf/isolation/Isolation2007.pdf *HICPAC is a federal advisory committee of infection control experts who provide advice and guidance to the Centers for Disease Control and Prevention (CDC) and the Secretary of the Department of Health and Human Services (HHS) regarding the practice of health care infection control, strategies for surveillance and prevention and control of health care associated infections in United States health care facilities.


• AIA Guidelines The AIA Academy of Architecture for Health (AAH) develops documentation, and disseminates knowledge to educating healthcare architects and other related constituencies; advancing the practice of healthcare architecture; improving the design of healthcare environments. For further information their web site is www.aia.org The guidelines can be purchased from “The Facility Guidelines Institute | 1919 McKinney Avenue | Dallas, TX 75201” (FGI) web page for purchase is www.fgiguidelines.org/pasteditions.html.


• The Facility Guidelines Institute now has responsibility for the “Guidelines for Design and Construction of Health Care Facilities”. The publication is revised every four years further information about FGI and the 2010 Guide is available from http://www.fgiguidelines.org/index.html. The 2010 Guide is published by the American Society for Healthcare Engineering (ASHE) and incorporates ANSI/ASHRAE/ASHE Standard 170-2008, “Ventilation of Health Care Facilities”. For further information about ASHE contact http://www.ashe.org.

Reduction of Nosocomial Infections

Recently saw an article in the “Archives of Internal Medicine” showing an alarming statistic for nosocomial infection. The report indicates 1.7 million hospitalizations contract health care associated infections each year, costing billions of dollars and thousands of deaths.

Nosocomial transmission in hospitals occurs by several routes and some microorganisms may be transmitted by more than one route. The four main transmission routes in hospitals are by contact, droplet, airborne or common vehicle. If we could just reduce a small percentage of these occurrences there could be a huge savings of healthcare cost, suffering and life.

Maybe there is a way to make some headway into reducing these cross infections that are transmitted by airborne droplet nuclei. Millions of dollars of taxpayer’s money has been allocated through government grants to hospitals for the purchase of HEPA air purification to be used in the event of medical emergency. Much of this equipment is in storage awaiting emergency deployment.

Would it not make sense, to take this equipment from storage and strategically deploy it around the health care facilitys thereby reducing the concentrations of airborne infections? This reduction of infectious particles would help patients that have compromised immune systems to resist some of the nosocomial infections. In the event of a pandemic or act of terrorism the equipment could still be redeployed to other locations within the health care facility.