California Code of Regulations › Title 17 - Public Health › Division 3 - Air Resources › Chapter 1 - Air Resources Board › Subchapter 7.5 - Airborne Toxic Control Measures › Appendix 2 - Method for Measuring Inward Face Velocity

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
Inward face velocity must be measured at least once every
					 calendar year and whenever the air pollution control system is changed in any
					 way that may impact air flow to ensure that the ventilation system is working
					 properly. Measurements must be conducted in accordance with the procedures
					 specified in this Appendix 2 or an alternative method approved by the
					 permitting agency.
1. Hood
				  Measurement:
Divide the face of the hood, the slot area, or the normal
					 plane, at the capture velocity measurement point into equal area rectangles
					 (see Figure 1). The side of each rectangular area should be no longer than 12
					 inches. Measure the air velocity (fpm) at the center of each rectangle using a
					 calibrated anemometer or other measuring device approved by the permitting
					 agency. The velocity measuring device must have an accuracy of at least +10% of
					 full scale. The measuring device must be in good condition, of proper velocity
					 range, and operated according to the manufacturer's instructions. The measuring
					 device must be calibrated in accordance with the manufacturer's
					 recommendations. Do not block or disturb the airflow while taking the
					 readings.
Image
Figure 1: Airflow distribution measurement for an exterior
					 hood and an enclosing hood
Measure the volumetric airflow rate through the hood by
					 measuring the velocity at the center of each equal-sized rectangular area
					 (i.e., by performing pitot traverses.) If no suitable location exists for
					 performing complete pitot traverses, measure the slot velocity and use this
					 data to estimate the volumetric airflow rate through a hood.
2. Walk-in Booth Measurement:
For a cross-draft walk-in booth (i.e., air enters through
					 filters in the front of the booth and leaves through filters in the back of the
					 booth):
Divide the length of the booth into at least three
					 cross-sectional areas to obtain the velocity profile in the booth. One
					 cross-sectional area must be located near the exhaust plenum, one close to the
					 supply plenum, and the other in the middle of the booth. Figure 2 illustrates
					 the location of cross-sectional areas. Record the distance between each
					 cross-sectional area and the exhaust or supply plenums. The distance between
					 each cross-sectional area must not exceed ten feet.
Lay out imaginary grid lines through each cross sectional
					 area. Use the intersections of the grid lines as locations to measure
					 velocities inside the booth. The intersection points must be no more than six
					 feet apart. Record the location of each point on the grid. Measure the air
					 velocity (fpm) at each intersection point on the grid using a calibrated
					 anemometer or other measuring device approved by the permitting agency. The
					 velocity measuring device must have an accuracy of at least +10% of full scale.
					 The measuring device must be in good condition, of proper velocity range, and
					 operated according to the manufacturer's instructions. The measuring device
					 must be calibrated in accordance with the manufacturer's
					 recommendations.
Image
Figure 2: Airflow distribution measurement inside a
					 cross-draft walk-in booth
For a down-draft walk-in booth (i.e., air enters through
					 filters in the ceiling of the booth and leaves through filters that cover
					 trenches under a metal grate floor):
Divide the height of the booth into at least three
					 cross-sectional areas to obtain the velocity profile in the booth. One
					 cross-sectional area must be located near the exhaust plenum, one close to the
					 supply plenum, and the other in the middle of the booth. Record the distance
					 between each cross-sectional area and the exhaust or supply plenums. The
					 distance between each cross-sectional area must not exceed ten feet.
Lay out imaginary grid lines through each cross sectional
					 area. Use the intersections of the grid lines as locations to measure
					 velocities inside the booth. The intersection points must be no more than six
					 feet apart. Record the location of each point on the grid. Measure the air
					 velocity (fpm) at each intersection point on the grid using a calibrated
					 anemometer or other measuring device approved by the permitting agency. The
					 velocity measuring device must have an accuracy of at least +10% of full scale.
					 The measuring device must be in good condition, of proper velocity range, and
					 operated according to the manufacturer's instructions. The measuring device
					 must be calibrated in accordance with the manufacturer's
					 recommendations.
3. Average
				  Value of Readings
Calculate the average value for all velocity readings, if
					 all individual readings are within +20% of the average value. Do not include
					 turbulent readings when calculating the average (turbulent airflow may be
					 indicated by negative or zero velocity readings.) Record and make available for
					 inspection by the permitting agency the entire velocity profile to show the
					 airflow distribution. Examples:
Hood A - Velocity Readings (fpm)
100
90
110
85
115
100
105
95
100
Average Velocity =
900 fpm / 9 =
100 fpm
Hood B - Velocity Readings (fpm)
200
200
0
200
50
0
100
-5 *
-45 *
Average velocity =
750 fpm / 7 =
107 fpm **
* Negative values indicate airflow in reverse direction and
					 are not included in the average.
** This is not a valid average, because individual readings
					 are not within +20% of the average. The booth airflow needs to be adjusted and
					 balanced before the velocity is measured again.