Air filtration: Meeting clean air requirements in hospitals

Effective air filtration is highly desirable in hospitals, in particular in areas with critical air quality requirements, such as childrens' wards and Cancer Research Centres. Hospitals are often located in congested urban areas which poses the problem of preventing smoke, diesel and other hydrocarbon emissions from entering the hospital environment. Mycelx undertook studies at a hospital in Georgia, USA to check the effectiveness of its air filtration systems.

Soot residue from the hospital generator
Soot residue from the hospital generator
Generator exhaust and air intake
Generator exhaust and air intake
Table of captured organic compounds
Table of captured organic compounds
Mycelx filters and target membranes were placed over the hospital's air intake
Mycelx filters and target membranes were placed over the hospital's air intake
The Mycelx filters after two months
The Mycelx filters after two months

The Northeast Georgia Health System (NGHS) serves more than 700,000 people from more than 15 counties in northeast Georgia in the USA. A full range of health care services is offered through two hospital campuses including advanced cardiac care.

The hospital is located by a busy road with construction underway and is surrounded by car parks and periodically employs a high-powered diesel generator for back-up power. The diesel engine emits fumes which are then drawn into the hospital by the air handlers. Intake air also has pollutants from parking areas and construction activities. The hospital was experiencing unacceptable air qualities in certain areas of the hospital due to intake of toxic and odiferous compounds from these various sources.

Contributing factors to the odours included construction at the hospital, ambient traffic, emissions from diesel vehicles, evaporative materials and volatile organic compounds present in construction materials such as glue, for example. Additionally, facilities staff described further problems, including that the air intake always had to be turned off when the diesel generator was activated. If the air intake was not turned off, there were immediate complaints from inside the hospital. The diesel generator usually operated two to three times a month for 3-4 hours each time.

Looking for a solution?

Mycelx engineers inspected the air processing equipment and filters with facilities staff at the hospital, and both parties agreed on the strategic placement of filters and target membranes in order to gauge the possible beneficial impact. Specifically, filters were placed at the air intake immediately adjacent to the exhaust of the diesel generator and in the air intake to the administrative building (the air to this area is drawn from the car park).

The diesel generator was activated approximately ten times within a period of three months without de-activating the air intake. Filter samples were collected by Mycelx and analysed for hydrocarbons by GCMS using headspace and extractive techniques.

The results

As a result of the action taken, Mycelx and the NGHS analysed the performance of the filters. Firstly, it was necessary to monitor the detection of odours by hospital staff during operation of the diesel generator. The diesel generator was operated approximately 10 times at 3-4 hours per event over a period of three months without disabling the air intake directly above the diesel exhaust. The staff were not informed. However, no complaints were registered with facilities regarding the ambient air quality.

Organic removal on the Mycelx filters was shown to capture approximately 2-3 times the number of compounds detected on standard filters (see Table 1). The oil holding capacity for the Mycelx filters also proved to be in excess of nine times that of the standard filters, while the percentage arrestation and particle holding capacity were found to be approximately double for the membrane filters compared to standard filters. Finally, hospital staff also reported that the Mycelx CPS membranes were found to be successful in arresting smoke particles caused by wildfires in South Georgia.

Hydrocarbon categories

The captured hydrocarbons fell into two major categories. Firstly, the diesel and gasoline range included semi-volatile organic compounds and the products of their incomplete combustion. Secondly, there were solvents and plasticizers, which are present in cleaning compounds and construction materials. As expected the administrative building intake had a higher proportion of solvents and plasticizers. The diesel intake also had many of the solvents and plasticizers present in the Corporation administrative building intake, as well as a higher proportion of products of incomplete combustion.

Odours are often organic compounds. Once generated these compounds tend to agglomerate in complex ways. Often these compounds are not in the gaseous state but are incorporated into complex assemblages of droplets and particles. Simple interception is often not sufficient to capture such materials due to the surface tension of the aerosolised pollutant. This is why standard particle type filters and even carbon filters are not able to eliminate odours.

Mycelx filters incorporate chemical affinity into the fibres and are able to breach the microcellular membrane of the aerosol and incorporate the captured organic compounds. Based on the results and the observational report from facilities staff at the hospital, it appears that the chemical affinity of Mycelx filters for aerosolised hydrocarbons was able to reduce ambient levels within the hospital to below odour detection limits, even when the diesel generator and air-handler were both in use. Chemical analysis indicates that certain classes of organic compounds were removed by Mycelx filters which were not removed by the standard hospital filters.

Some interesting examples are complex products of incomplete combustion such as cis-1-butyl-2-methylcyclopropane, which is the product of partial combustion of 2,2,4-trimethyl pentane – a major constituent of gasoline often referred to as octane. Another group of compound not captured by standard filters was low vapour pressure solvents and plasticizers, which are often components of cleaners, plastics and binding agents. One example is N-formylmorpholine.

This facility is challenged with a relatively high amount of semi-volatile organic compounds and products of incomplete combustion even when the diesel generator is not in operation. This is probably due to construction and the high volume of car and truck traffic around the hospital. Engagement of the diesel generator exacerbates the situation. The findings demonstrated that the high degree of ambient organics in the air around the hospital lends itself to the use of Mycelx air filters in all the hospital air handlers.

How do the filters work?

According to Mycelx, its air filters and membranes are able to permanently capture and immobilise organic aerosols at very low pressures. Conventional air filters, even HEPA/DOP rated, are unable to capture these species and often re-entrain the intercepted aerosols resulting in more robust droplets emerging from the other end.

Anthropogenic organic aerosols are visible as a consistent haze around populated areas and are the result of gasoline and diesel emissions and VOCs generated by manufacturing and construction activities. The aerosol droplets are often complex assemblages of sub-micron particulate matter and semi-volatile and volatile range hydrocarbon components.

Conventional filter fibres, which are essentially intended to function as particle interceptors, have little affinity for most of the organic components of aerosols and often tend to act as surfaces which facilitate evaporation and re-entrainment. This results in poor air quality. On contact with Mycelx treated fibres the organic compounds are instantly rendered to a cohesive Viscoelastic mass, which is incapable of re-entraining or evaporating. This property is particularly useful in hospital settings where multiple factors result in problematic air. These factors include but are not limited to:

• Diesel generators which are in periodic or frequent use in hospitals;

• Urban environments;

• Construction;

• Patient perceptions – patients expect hospital air to be better and safer than air in other buildings. As a result they are often upset when they detect fumes and odours from outside. This is the case because hospital filters are more or less the same as the filters most people use in their homes.

Contact: Mycelx Technology Corporation, 470 Woods Mill Road, Gainesville, GA 30501, USA, Tel: +1 770 534

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