“In Door Air Quality in Hospitals, Photo Catalytic Oxidation Technology for air purification”
Hospitals are one of the fundaments of the society in a country and patient comes to the Hospitals to get treatment and regain health. When designing a HVAC system for a Hospital there are several key parameters to take into account:
- Reduce Hospital Acquired Infections
- Ensure HVAC Energy Savings
- Lower labor, maintenance and disposal cost
- Achieve sustainability
This paper focuses on the reduction of Hospital Acquired Infections, and discusses various aspects of dilution, filtration and air purification in Hospitals. The main part describes the use of Photo Catalytic Oxidation Technology for air purification in hospital facilities. At the end of the article a brief presentation of the product ZAND-AIR PCOC™3 is included.
The nature of the people and the process taking place at hospital needs to be understood and taken into consideration when designing HVAC system for optimal In Door Air Quality (IAQ). Patients and health care practitioners can carry biological pathogens (bacteria, virus and fungi) which can be transmitted to peers. Some of the patients are immunosuppressed . Through surgical operations and other activities in Operating Theaters (OT) patient are exposed due to open wounds and surgical scars. There has been an ongoing debate between professionals if Infectious diseases are airborne or not over the past decade. ASHRE has reviewed the available literature and published a position document in 2009, stating that many infectious diseases can be airborne, and hence HVAC construction in Hospitals needs to be designed to prevent cross infections. (ASHRAE 2009)
“Many infectious diseases are transmitted through inhalation of airborne infectious particles termed droplet nuclei.”
“Airborne infectious particles can be disseminated through buildings including ventilation systems.”
More than 60 bacteria, virus and fungi are documented as infectious airborne pathogens. Diseases transmitted via bio aerosols include; Tuberculosis, Legionaries, Influenza, Colds, Mumps, Measles, Rubella, Small pox, Pneumonia and Meningitis (Saito 1992). One of the most common and harmful bacteria’s which can be found and transmitted in Hospitals are Methicillin Resistant Staphylococcus Aureus (MRSA). The prevalence of MRSA in Hospital in Indian has been reported to be 27% in Bombay, 43% in Delhi and 47% in Bangalore. (Metha 1996) The prevalence of MRSA in India was reported in one study to increase from 12% in 1992 to 80.83% in 1999. (Werma 2000). Once introduced into a hospital MRSA frequently becomes endemic, difficult to control, expensive to treat and often very difficult to eradicate. MRSA causes major morbidity and mortality. MRSA was reported to cause 19,000 deaths 2008 in the U.S and a patient who contracts it while hospitalized stays an average 10 days longer and costs an additional $30,000. (JAMA 2010).
While 1 in 10 people have the MRSA bacteria on their skin, and don't necessarily become sick from it, a new superbug, NDM-1 is now appearing in hospitals in the U.K and the U.S. It has quickly become one of the most feared infections. NDM - 1, discovered in New Delhi (hence the name New Delhi metallobeta-lactamase, or NDM-1) makes bacteria resistant to antibiotics. (Walsh 2011)
Dilution and air Distribution
There are two basic physical principles behind the roles of ventilation in infection control. The first is through dilution of airborne pathogens, and the second is the control of movement of airborne pathogens from one space to another in the hospital operating room. Opinions vary regarding the importance of airborne contamination with respect to post-operative infection. It is generally agreed that the majority of infections are caused by contact contamination from the patient themselves or the surgical team. Studies have also indicated a relationship between the incidence of infection and the level of air contamination. While the validity of these results can be discussed due to changes in surgical gowns, surgical techniques, antibiotics, etc., the consensus is simply that the air should be kept as clean as possible. The largest sources of contamination in a sterilized operating room, with a clean air supply and isolation from adjacent areas, are the surgical team and patient. The function of the operating room’s air distribution system therefore must be to carry away any contaminants expelled into the air by either the surgical team or the patient on the operating table. The system must also isolate and remove this contaminated air so it cannot mix with the clean supply air.
The simplest way to reduce the airborne contaminants present in the operating room is to increase the air ventilation rate. Minimum air changes per hour are defined by ASHRAE, AIA and ASHE for most of the areas in a Hospital. There seems to be a consensus for a minimum of 12-15 ACH in critical areas of hospital like Operation Theaters, ICU and Protective Environment rooms. For less critical areas in a hospital the recommendation is 4-6 ACH. In general 2-3 ACH of fresh air is demanded, which ensures good air quality and gives the possibility of energy savings through recirculation of a large amount of the air.
Laminar flow ventilation system was developed to provide a method of controlling the transport of air contamination by introducing the supply air into the operating room at low uniform velocities promoting a stable downward flow of air. Although laminar flow diffusers discharge air at low face velocity, some entrainment of room air still occurs. This entrainment in combination with the temperature differential of the supply air causes the air pattern to angle towards the center of the discharge air envelope. As a result a clean zone is created around the patient.
Another solution to disinfecting the air is to capture offending particles in a filter mesh of some kind. HEPA and ULPA filters are specifically designed for the collection of submicron PM (Particulate Matter) at high collection efficiencies. Key metrics affecting function are fiber density and diameter, and filter thickness. The air space between HEPA filter fibers is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Just as for membrane filters, particles so large that they are as wide as the largest opening or distance between fibers cannot pass in between them at all. But HEPA filters are designed to target much smaller pollutants and particles are mainly trapped (they stick to a fiber) by either interception, Inertial Impaction, Diffusion or Sieving.
The relevant size measurement used in aerosol science is the aerodynamic diameter. This diameter is usually different from the actual particle size of microorganisms, and accounts for the non-spherical nature of the cells. This parameter is more useful for predicting aerodynamic behavior of a particle in air. Viruses are the smallest, ranging in size from 0.01 µm to 0.4 µm, while fungal spores are at the upper end of the range and can be larger than 20 µm. Bacteria range in size from 0.5 to 10 µm.
Filtration is an effective way of controlling the aerobiology of indoor air. However reports show that microorganisms can grow on untreated air filters and even grow through the filters and release spores downstream. (Kemp 1995) Other studies have reported or shown that microbes can survive or grow on filters. Coincident with the problem of growth of fungi on filters is the possible generation of VOCs. Laboratory experiments proved that species of Aspergillus, Cladosporium, Acremonium, and possibly other microbes may produce acetone, ethanol, formaldehyde, acetaldehyde and other compounds on fiberglass and cellulose filter media (Schleibinger 1999). Furthermore HEPA filter has a substantial pressure drop which increases over time.
ASHRAE guidelines propose using two filter beds containing MERV 7 and HEPA filter in critical areas of a Hospital and two filter beds containing MERV 7 and MERV 13-14 in less critical areas in a Hospital. (ASHRAE 2011)
Purification - Photo Catalytic Oxidation
Several attributes of Photo Catalytic Oxidation make it a strong candidate for indoor air quality (IAQ) applications. Pollutants, particularly VOCs, are preferentially adsorbed on the surface and oxidized to (primarily) carbon dioxide (CO2). Thus, rather than simply changing the phase and concentrating the contaminant, the absolute toxicity of the treated air stream is reduced, allowing the photo catalytic reactor to operate as a self-cleaning filter relative to organic material on the catalyst surface. (Jacoby 1996) Bacteria and viruses are destroyed by the clastogenic effect of UVC. The process is called heterogeneous photo catalysis or photo catalytic oxidation. In chemistry, photo catalysis is the acceleration of a photoreaction in the presence of a catalyst. Titanium dioxide (TiO2) is a common catalyst for air purification. Titanium dioxide is a semiconductor photocatalyst with a band gap energy of 3.2 eV. When this material is irradiated with photons of less than 385 nm, the band gap energy is exceeded and an electron is promoted from the valence band to the conduction band. The resultant electron-hole pair has a lifetime in the space-charge region that enables its participation in chemical reactions. The most widely postulated reactions are shown here.
OH- + h+ _________> .OH
O2 + e- _________> O2-
Hydroxyl radicals and super-oxide ions are highly reactive species that will oxidize volatile organic compounds (VOCs) adsorbed on the catalyst surface. They will also kill and decompose adsorbed bio aerosols. (Goswami 1995)
The photo catalytic deactivation of bacterial cells has been widely reported in the literature. There is substantial evidence that the mechanism of cell killing with PCO is the damage of the cell membrane. (Blake 1999) The cell membrane contains unsaturated phospholipid and, therefore, is the potential target leading to lipid peroxidation. The detrimental impact of lipid peroxidation to all forms of life has been well documented in the literature. There is still conflicting evidence in the literature as to which reactive oxygen species are directly involved in the photo killing process.
ZAND-AIR PCOCTM 3
The ZAND-AIR PCOC TM3 has been developed for air purification in laboratories and medical facilities. The ZAND-AIR PCOC TM3 contains a MERV 13 filter, three Photo Catalytic Oxidation Chambers and an additional slot for a Potassium Permanganate Filter (PPF). The frame body of the ZAND-AIR PCOC TM 3 between flanges is: W 629 mm L 784 mm H 520mm
Each PCO Chamber contain of 2 UVC lights of 20 W with reflectors, illuminating a substrate of TiO2 nanoparticles. The ZAND-AIR PCOCTM3 use a patented process to affix TiO2 nanoparticles to a solid substrate, for this TiO2 to interact with UVC radiation at 253, 7 nm. To increase the efficacy of the PCO process three PCO chambers are placed sequentially in a single frame, thus increasing the dwell time for the airstream through the PCO-Chambers.
The pressure drop of three units of PCO chambers without MERV 13 and Potassium Permanganate Filter is:
The nominal air capacity for the unit is 2000 CFM. While the photo catalytic process is very fast the number of the photo catalytic actions occurring in the PCO Chamber are multiple and sequential. Using a high proportion of return air (>85%) as the part of the airstream is thus helping the cleaning process, as the return air already passed before through the photo catalytic oxidation process. From a service perspective the UV-lights needs to be changed every 12 month, and the MERV 13 and PPF filter every 6 months or sooner.
There have been reports in the literature of air purification products generating harmful byproducts such as ozone. A study has been performed to evaluate if any harmful byproduct is produced by the ZAND-AIR PCOC™3.
“The evaluated PCOC3-unit, operating with a UV-wavelength of 253.7 nm and a TiO2 catalyst showed no signs of ozone generation. Instead, the results indicate that ozone was captured by the device at a removal rate of 67 ach, corresponding to a single pass efficacy about 15%” (Kadrobegovic 2010)
The ZAND-AIR PCOCTM3 combines the efficacy of the UV-light and the Photo Catalytic Oxidation Technology. The below graph shows an example of a PCO system disinfecting air in a recirculation system. In this graph the disinfection due to UV alone is graphed for comparison. Based on comparison of the effective rate constants, the effect due to UV appears to account for 63% of the disinfection, while PCO accounts for an additional 37% reduction. (Goswami 1997)
Studies have been performed at the Polytechnic University in Hong Kong confirming the removal efficacy on biological pathogens of the Zandair product. A single PCO Chamber air purification system was operating in recirculation mode in a test room and the cfu/m3 levels (Colonizing Forming Units) was measured over time. After 120 minutes of operation a reduction from 111 to 7 cfu/ m3 was reported. (Chan 2004).
The ZAND-AIR PCOCTM3 has been successfully installed in In Vitro Fertilization (IVF) Laboratories since 2008. Culturing human embryos and cells is one of the most sensitive environments which has very high demands of clean air, free from VOCs and biological pathogens. Successful Installations of the ZAND-AIR PCOC™3 has been done in USA, Canada, UK, Spain, Ireland and India.
Photo catalytic reactors may be integrated into new and existing heating, ventilation, and air conditioning (HVAC) systems due to their modular design, room temperature operation, and negligible pressure drop. PCO reactors also feature low power consumption, potentially long service life, and low maintenance requirements. These attributes contribute to the potential of PCO technology to be an effective process for removing and destroying low level pollutants in indoor air, including bacteria, viruses and fungi.
ASHRAE 2009, position paper, Airborne Infectious diseases.
ASHRAE 2010, Ventilation of Health Care Facilities
ASHRAE 2011, Addendum to standard 170-2008 Ventilation of Health Care facilities
Blake 1999, Application of the photocatalytic chemistry of titanium dioxide to disinfection and the killing of cancer cells, Separation and Purification Methods Volume 28(1).
Chan 2004, Test Report, Hong Kong Polytechnic University
Dikema 2008, Preventing MRSA Infections: Finding is Not Enough JAMA, 2008:299(10): 1190-1192
Goswami, 1995, Photocatalytic disinfection of indoor air, Solar Engineering ASME 1995 1: 421-427
Jacoby 1996, Heterogeneous photocatalysis for control of volatile organic compounds in indoor air. Journal of Air & Waste Management 46: 891-898
Kadrogebovic 2010, Air Cleaning by Photo Catalytic Oxidation:An Experimental Performance Test, ASHRAE Transactions, Volume 117, Part 1.
Kemp, 1995 Growth of microorganisms on HVAC filters under controlled temperature and humidity conditions. ASHRAE Trans 101, 305-316.
Matusunga 1985, Sterilization with particulate photosemiconductor. Journal of Antibacterial Antifungal Agents 13: 211-220.
Mehta 1996, A pilot programme of MRSA surveillance in India. (MRSA Surveillance Study Group). J Postgrad Med 1996;42:1-3
Saito 1992, Mode of photocatalytic bactericidal action of powdered semiconductor TiO2 on Streptococci mutans. Journal of Photochemical Photobiology 14: 369-379.
Schleibinger 1999, Accumulation of endotoxins on air filters in heating, ventilating and air conditioning (HVAC) systems, Indoor air'99, Edinburgh, Vol 2, 243244.
Verma 2000, Growing problem of methicillin resistant staphylococci - Indian scenario. Indian J Med Sci 2000; 54:535-40
Walsh 2011, Dissemination of NDM-1 positive bacteria in the New Delhi environment and its implications for human health: an environmental point prevalence study, The Lancet Infectious Diseases, Volume 11, issue 5 Pages 355 - 362, May 2011.
Eliminating from the hospitals and medical laboratories any disease causing airborne pathogens and volatile organic compounds is critical for the safety and health of patients, employees, and those visiting these facilities. Zandair Air Purification equipment offers the best in hospital air purifiers and medical laboratory purification systems.
Infection Control Today (ICT) October 12, 2012 Newletter article "Superbugs Ride Air Currents Around Hospital Units" addresses the issue of airborne pathogens in Hospitals.
Hospital superbugs can float on air currents and contaminate surfaces far from infected patients’ beds, according to University of Leeds researchers. The results of the study, which was funded by the Engineering and Physical Sciences Research Council (EPSRC), may explain why, despite strict cleaning regimes and hygiene controls, some hospitals still struggle to prevent bacteria moving from patient to patient.
It is already recognized that hospital superbugs, such as MRSA and C. difficile, can be spread through contact. Patients, visitors or even hospital staff can inadvertently touch surfaces contaminated with bacteria and then pass the infection on to others, resulting in a great stress in hospitals on keeping hands and surfaces clean.
But the University of Leeds research showed that coughing, sneezing or simply shaking the bed linens can send superbugs into flight, allowing them to contaminate recently cleaned surfaces.
PhD student Marco-Felipe King used a biological aerosol chamber, one of a handful in the world, to replicate conditions in one- and two-bedded hospital rooms. He released tiny aerosol droplets containing Staphyloccus aureus from a heated mannequin simulating the heat emitted by a human body. He placed open petri dishes where other patients’ beds, bedside tables, chairs and washbasins might be and then checked where the bacteria landed and grew.
The results confirmed that contamination can spread to surfaces across a ward. “The level of contamination immediately around the patient’s bed was high but you would expect that. Hospitals keep beds clean and disinfect the tables and surfaces next to beds,” says Dr. Cath Noakes, from the University’s School of Civil Engineering, who supervised the work. “However, we also captured significant quantities of bacteria right across the room, up to 3.5 meters away and especially along the route of the airflows in the room.”
“We now need to find out whether this airborne dispersion is an important route of spreading infection,” adds co-supervisor Dr. Andy Sleigh.
The researchers are hoping that computer modeling will help them determine the risk. The findings have been compared to airflow simulations of the mock hospital rooms and the research team have shown that they are able to accurately predict how airborne particles can be deposited on surfaces.
“Using our understanding of airflow dynamics, we can now use these models to investigate how different ward layouts and different positions of windows, doors and air vents could help prevent microorganisms being deposited on accessible surfaces,” says King.
The international design and engineering firm Arup, which designs hospitals, part sponsored the study. Phil Nedin, director and global healthcare business leader at Arup, says: “We are looking at healthcare facilities of the future and it is important that we look at key issues such as infection control. Being involved in microbiological studies that inform airflow modeling in potentially infectious environments allows us to get a clear understanding of the risks in these particular environments.”
The paper, “Bioaerosol Deposition in Single and Two-Bed Hospital Rooms: A Numerical and Experimental Study,” was published in the journal Building and Environment.
This research is funded by an EPSRC Challenging Engineering grant held by Dr. Cath Noakes. Marco-Felipe King’s PhD was also partially sponsored by Arup.
Reference: M.F. King, C.J. Noakes, P.A. Sleigh, M.A. Camargo-Valero. Bioaerosol Deposition in Single and Two-Bed Hospital Rooms: A Numerical and Experimental Study. Building and Environment. 2012.
Source: University of Leeds
Airborne Infections in Nursing Homes is of great concern to the staff, patients, and loved ones. When a person is unable to care for themselves independently and family members are overwhelmed, unprepared, or unable to give the kind of care their loved one needs to insure a good quality of life a Nursing home may be the best alternative. When deciding which long term care facility would best fill the needs of the individual one concern that may not be in the forefront is airborne infections. While overall physical appearance of a nursing home is extremely important it is what you cannot see that perhaps can be the most critical element for the physical health of the employees, caretakers, and residents. The potential infectious pathogens in the ambient air can be a major source of infection and disease in long term care facilities.
“Almost as many nosocomial infections occur annually in nursing homes as in hospitals in the United States1 (Haley et al 1985).
Potential airborne infections in Nursing Homes include viruses such as Adenovirus, Coronavirus, Coxsackievirus, Influenza, Metapneumovirus, Norwalk virus, Parainfluenza, Rhinovirus, Rotavirus, and RSV. The sources of most of these are humans. Norwalk virus and Adenovirus are said to be from the environment. All of these along with many bacteria are listed in Wladyslaw Kowalski's book 'Hospital Airborne Infection Control' page 218. Some of the more common bacteria listed in this book are MRSA, Streptococcus pheumoniae, Mycobacterium tuberculosis and VRE.
Filtering and purifying the air in hospitals and nursing care facilities is of vital importance to the overall health and well being of caretakers as well as patients or residents. Photocatalytic Oxidation is one of the best technologies utilized for air purification.
1. Hospital Airborne Infection Control; Wladyslaw Kowalski
From DailyMeHealth on twitter:
MRSA Infections Bringing More Children to Hospital http://dmne.ws/rnT0DB (http://twitter.com/DailyMeHealth/statuses/101692448509665280)
MRSA airborne bacteria are causing more children to go to the hospital. Most people think MRSA airborne is only contracted at the hospital but the surrounding community can also be a place filled with potential MRSA airborne bacterial infection.
Schools are very susceptible for MRSA airborne bacteria outbreaks. Let's face it bacteria is everywhere in our environment and it does not necessarily cause us harm. When the skin is broken by abrasions, cuts, scrapes, or more serious wounds, bacteria may enter the body. MRSA airborne is a more significant problem because it has mutated over time and is much harder to destroy with antibiotics.
Enclosed areas such as schools, hospitals, elder care facilities, or office buildings, have a more concentrated amount of people and germs. It is so important to keep these areas as clean as possible. Air and surfaces, need to be cleaned and sanitized on a regular basis to significantly reduce the spread of MRSA airborne bacteria and many other malignant microbes.
Children need to be instructed before they head off for school, not to share towels or clothing, and avoid contact with anyone with open wounds. It is important to keep wounds covered as well, lessening the chances of bacteria entering the wound. And don’t forget hand washing with soap and water for 15 seconds will help immensely in keeping those nasty germs at bay as well.
Ask your school and hospital to install equipment into their AC system that destroys airborne MRSA, so it can not settle on you with the draft of air conditioned air.