MONITORING OF HEPA FILTERS

ST — 068
MONITORING OF HEPA FILTERS


Air supply to the sterile area must be appropriately filtered to minimize the potential contamination by both viable and nonviable particulate matter. HEPA filters are used to filter the air, both at terminal points of blowers and in laminar flows where product will be expressed. The HEPA Filter fixtures are to be monitored periodically by the following tests to check that they maintain their rated efficiency.

1. Air velocity
2. Pressure drop across HEPA filters
3. Checking integrity of HEPA filter using cold DOP
4. Air direction

In addition to monitoring the filter surface, the seal of each filter element to its frame and the seal between the filter frame and the filter housing must be verify that particles are not escaping around the filter.

1. Air Velocity Measurement of HEPA Filters

Air velocity of laminar flow hoods is measured to assure an acceptable level airflow in the sterile area, component preparation area, and all terminal HEPA filters are to be monitored.

Equipment Used: Alnor Velometer no. 600 P

PROCEDURE

In case of laminar flow hoods, measure the air velocity by positioning the velometer probe at a distance of one foot above the work surface. Read velocity directly from the meter and record. Six reading should be taken and the average calculated.

In case of terminal HEPA filters, the velocity should be taken six inches away from the grill and six readings should be taken and averaged and these reading should be taken for calculating air changes in the room.

ACEPTANCE CRITERA
A minimum air velocity at work surface of 0.3 meters/second (i.e. 60.0 ft/minute) for vertical laminar flow hoods and a minimum velocity of 0.45 meters/second (i.e. ft/minute) for horizontal laminar flow hoods.

*If velocity drops below the acceptable criteria, replace the filters

Frequency of test: Quarterly

2. Procedure For Measuring Pressure Drop Across HEPA Filter

The amount of pressure drop across terminally mounted or laminar flow hood HEPA filter is related to the particulate loading of the filter or the amount of blocking of the filter output. The life of HEPA filter can be improved by cleaning the pre-filters in air handling units frequently. When the pressure drop across the HEPA filter reaches above the limit, the filter must be changed. Limit: 2’’ of water gauge (i.e. 50.8 mm of water gauge)

PROCEDURE

EQUIPMENT

1. Two sampling tubes, one upstream of the filter and one downstream.
2. Calibrated Magnehelic gauges or inclined manometer (zero adjusted)

Place one end of the sampling tube in the upstream of the filter under test, and connect the other end to the inlet of the calibrated Megnehelic or inclined manometer. Place one end of the other sampling tube downstream of the HEPA filter and the other end to the outlet of the Megnehelic gauge or inclined manometer, and record the reading directly from the Megnehelic gauge manometer.

Frequency of Testing: Quarterly

Limit = pressure drop not more than 2 inches of water gauge (i.e. 50.8 mm of water gauge). If the pressure drop is more than the limit, the filter has to be replaced.

3. 3. Procedure For Checking Integrity Of HEPA Filter Using DOP

Air supply to the sterile area must be appropriately filtered to minimize the potential contamination by both viable and nonviable particulate matter. HEPA filters are used to filter the air, both at terminal points of blows and in laminar flow where product will be exposed. To check the efficiency of particulate retention, the HEPA filter fixtures are to be monitored. The porosity of HWPA filter is 0.3 micron. Therefore, aerosol of DOP can be used to check the efficiency of retention since it has an average particle size of 0.45.

PROCEDURE
Start the system and introduce DOP in the upstream of the HEPA filter. Scan the down stream flow with suitable light scattering photometer which detects the DOP particles. Whole of filter surface and filter frame/housing to be scanned. Any leakages if observed, to be mentioned in a diagram and can be rectified, if leaks are within limit.

Frequency of integrity testing DOP of HEPA filters using DOP is at least once a year or when there is any replacement of filter, gasket housing etc.

Acceptance Limit is = 99.997% retention of particles.

Direction of Air-flow

Direction of air-flow of all terminal HEPA filters and HEPA filters of all laminar flow hoods are also monitored using smoke stick Titanium Tetrachloride (TiCl4). The smoke sticks are moved in front of the HEPA filters to note the direction of the airflow to confirm that the movement is in straight line and that there is not turbulence at critical areas of operation.