filtration

The National Institute for Occupational Safety and Health (NIOSH) has undertaken a long-term performance test of heating, ventilation, and air-conditioning (HVAC) system filters. This testing is being conducted at the NIOSH facility in Morgantown, WV in an air handling unit (AHU) that services the animal quarters. The six-pocket bag filters in this AHU have been replaced with higher efficiency mini-pleat V-Bank filters and have been monitored monthly for filtration efficiency.

Air quality begins with good engineering air handling system (HVAC) controls. Air handler filters should remove the major particulate matter from incoming ambient air. A study of various NIOSH air handler bag filters was conducted to determine their filter efficiency against submicrometer particles (0.03-0.4 micrometers), since submicrometer particles are the most penetrating. Aerosol penetration measurements show an extremely large range of filter efficiency.

Several indoor air biofilters containing higher plants, mosses and microbes have been incorporated into functional offices, where they are a supplemental means of controlling indoor air quality through the removal of volatile organic compounds. In theory a rich microbial community indoors may in fact lower air quality through the production of microbial agents such as spores or aerial bacteria. Questions have arisen regarding the impact of an indoor air biofilter on ambient spore concentrations including the pathogen Legionella pneumophilia.

In buildings with mechanical ventilation, particles accumulate in the supply air filters. We conducted a field experiment in a school to investigate if such pollutants could affect the health of the pupils. In a school building we changed old and new supply air filters in the air handling units, with a cross over design of the study. Pupils answered a symptom questionnaire, and a subset of pupils was also examined by objective clinical methods.

Maintenance workers expressed concern of a potential health hazard due to a strong odor from used ventilation filters during routine maintenance at a research facility. This prompted a thorough examination of the physical and chemical nature of the filters and collected particulate matter. Light and electron microscopy indicated a predominance of opaque small particles, mostly in the submicrometer range. Many were agglomerations of smaller, roughly spherical subunits, consistent with combustion aerosol.

A variety of strategies have been implemented to protect nonsmokers from second hand smoke; these include separation or restricting smoking to selected areas, installation of air cleaners, increased ventilation, and outright prohibition of smoking. The concentrations of nicotine were measured and examined in different venues as a function of the techniques employed.

Airborne particle size distribution depends on the type of source from which the particles originate - filtration efficiency in turn, is dependent on particle size. Thus, in order to optimise filtration efficiency, it is important to gain knowledge on both: the size distribution of particles in the air to be filtered and the relationship between filtration efficiency and particle size. In addition, assessment needs to be made about the expected concentration level of particles around the building envelope and its time variation.

Measurements of indoor air quality indicators (temperature, humidity, dust, biocontaminants and CO2) were performed monthly during one year in a French office building. Air filters of the air handling unit of the building have also been characterised on site and in laboratory. Detailed results of these measurements are given and analysed.

A 2x2 replicated field intervention experiment was conducted in a call-centre providing a public telephone directory service: Outdoor air supply rate was 8% or 80% of the total airflow of 430 L/s providing 3.5 h-1; and the supply air filters were either new or used (i.e., used in place for 6 months). Each of these 4 conditions was maintained for a full working week at a time. Room temperature and humidity averaged 24 C and 27% RH.

A test protocol for the determination of fractional filtration efficiency of electrostatic precipitators was developed in order to determine the changes in efficiency of these appliances in real life, due to reduced corona discharge from the ionizing wires, and to define an accelerated laboratory method reproducing the real life vapor deposition process leadiong to the coating of the wires.