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RR 1 Box 480
Garrison, New York 10524
TEL: (914) 424-4077
FAX: (914) 424-3482

July 12, 1993

RE: Investigation of Isolation Room with the MICROCON® HEPA Filtration System.

An investigation was made into the effectiveness of the MICROCON HEPA Air Filtration System. A description of the equipment is included in this report. The survey involved sampling the air for microbiological viable organisms and total particulate levels. The samples were taken before running the MICROCON® and while the equipment was running. The results indicate that the MICROCON® HEPA Air Filtration System was effective at removing airborne particulate material and viable microbological organisms. These results appear to support the manufacturers claim that the filtration system will remove airborne droplet nuclei produced by persons actively infected with tuberculosis.


Over the past decade the incidence of respiratory tuberculosis (TB) infection has increased steadily in the New York Metropolitan area. Many hospitals in Newark have treated patients with actively infectious TB. Patients with active cases of TB can release infectious droplet nuclei containing TB into the air thereby exposing health care personnel in proximal areas. The risk of infection to the exposed persons is related to the quantities of TB bacillus in the air, the duration of exposure, and the general health of the individual. The Centers for Disease Control (CDC) has a criteria document that suggests methods that may reduce the risk of TB exposure. These methods include;

  1. Using isolation rooms for infectious persons. These rooms should be under negative pressure to the surroundiong areas and should receive a minimum of 6 air changes per hour
  2. Providing adequate ventilation to reduec concentrations of TB in the air.
  3. Using High Efficiency Particulate in Air (HEPA) filtration systems for recirculated air.
  4. Using ultra violet lamps to kill airborne TB
  5. Provide respiratory protection to expand individuals in high risk areas such as isolation rooms.

This survey involved the evaluation of the MICROCON® Air Filtration System. This system consists of a fan that pulls air into the top of the equipment through a HEPA filter and discharges the air back into the room through the base of the equipment. The unit separates at the three fan settings.

  1. 725 cubic feet per minute (cfm)
  2. 675 cfm
  3. 400 cfm

For a patient room that is 12 foot square and with a 8 foot ceiling this unit would provide over 20 air changes per hour at the lowest setting.


Air sampling was conducted following NIOSH method 500 for total particulate in air. The 5.0 micron poly vinyl chloride (PVC) filters were preweighed by the ITT Hartford Environmental Lab in Hartford CT. This is an AIHA accredited laboratory. The Lab report from Hartford Lab is attached to this report.

Fungi samples were collected on 3% malt extract agar using Anderson N6 single stage impaction sampler operated at a flow rate of 28.31 pm. Samples were collected using the N6 impaction sampler. Sample Petri dishes were prepared and analyzed by P&K Microbiology Services of Cherry Hill, NJ.


Both the dust samples and the fungi samples indicate a reduction in airborne particulate levels. Table I summarizes the dust level sampling results. Levels prior to operating the air cleaner were 180 micrograms per cubic meter of air. After running the air cleaner levels were below the limit of detention of 10 mcg/m.

Table II summarizes the bioaerosol monitoring the fungi levels in air. Levels were reduced from 40 cfu/m prior to running the air cleaner to between 5 and 7 cfu/m after running at low speed for approximately 1 hour.


The room tested is designed to operate as an isolation for Tuberculosis patients. The room is designed to have 6 air changes per hour and is under negative pressure to the hallway. This design is adequate for preventing the speed of airborne TB to the corridor, but it does not appreciably reduce the level of airborne contaminants inside the room. Operating the air cleaner in the room reduced levels of particulate and bioaerosols.

The results of this monitoring survey indicate the ability of HEPA filtration devices to reduce overall bioaerosol levels inside the isolation room. These results are consistent with our findings in a similar test conducted in May 1993. Although we have not used the system on TB, we believe the results support the contention that these air filtration devices are effective at reducing airborne droplet nuclei.

There is no single way to protect persons from TB transmission and it is recommended thata combination of methods be used. These sample results indicate that the HEPA filtration in combination with negative pressure in isolation rooms will provide an improved level of protection to the medical staff.

It should be noted that the MICROCON® Air Filtration System is an effective means of lowering the levels of bioaeosols in the air. There is no engineering controls that will eliminate TB exposure in the isolation room.

If you have any questions or need additional information, please feel free to call me at your convenience.


Edward Olmsted, CIH, CSP


Airborne Particulate Sampling
Room Tested

Sample No. Description Results

14024 Pretest- in room prior to operating the
MICROCON® Air Filtration System

14023 Pretset - in the hallway outside room prior
to operating the MICROCON® Air Filtration System

14021 After operating the MICROCON®
Air Filtration System inside the room
Below 10

14016 Field Blank <25 ug per filter

* ug/m3 indicates micrograms per cubic meter
(2) all sample results are corrected by subtracting the blank quantity.

Microbial Evaluation
Room Tested

Sample No Location - Description Species

9306281 Inside room, pretest; before running
the MICROCON® air cleaner
141.5 liters

9306282 Outside room, pretest; before running the MICROCON® air cleaner
141.5 liters
cladosporium 14.1

9306283 Field Blank no growth  

9306284 Inside room after turning on
the MICROCON® air cleaner
141.5 liters
no growth <5

9306285 Inside room after turning on the Microcon® air cleaner
198.1 liters
cladosporium 5

9306286 Inside room after turning on the MICROCON® air cleaner
424.5 liters
sterile fungi



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