Module Monitoring and Measuring Human External Exposure Calibration

Module Monitoring and Measuring Human (External) Exposure: Calibration Instruments and Techniques Exposure Science Monitoring Techniques Michael Bisesi, Ph. D, REHS, CIH Senior Assoc. Dean, Academic Affairs Director, Center for Public Health Practice Assoc. Professor, Environmental Health Sciences

Module: Calibration of Active Flow Air Sampling Pumps Objectives: § Discuss concepts of pre-sampling and post-sampling calibration of air monitoring instruments § Set-up various “calibration trains” § Conduct fundamental calibration using manual and electronic flow meters References: § Bisesi, M. (2003, 2 nd ed. ). Bisesi & Kohn’s Industrial Hygiene Evaluation Methods. CRC press/Taylor & Francis Publishers. Boca Raton, FL. § CDC/NIOSH Manual of Analytical Methods. http: //www. cdc. gov/niosh/docs/2003 -154/

Calibration: PURPOSE § Air sampling pumps must be calibrated to assure that the sampling flow rate of air is accurate. § Based on knowledge of the air flow rate of the pump and the duration of sampling, the total volume sampled can be calculated. § Ex: air sampling rate of 2 L/min, sample for 12 min… 2 L/min x 12 min = 24 L sampled

Calibration: PURPOSE § Air volume is the amount of air that literally flowed through a collection media. This is important for integrated or continuous sampling procedures so that concentration of a contaminant can be calculated. § Concentrations are based on the amount of contaminant collected, detected and measured in the sampling medium divided by the volume of air that flowed through the sampling medium. § Concentration = amount collected/detected/measured/volume of air

Calibration: PRE- and POSTSAMPLING § Calibration involves adjusting pumps to a specific flow rate and measuring against a standard. § Always calibrate pump with representative media in -line § Air sampling pumps must be calibrated both preand post-sampling § Flow rates are usually expressed in units of liters per min (L/min) and cubic centimeters per minute (cc/min) § Flow rates from pre- and post-sampling calibration must be within ± 10% of each other, but a difference no greater than ± 5% is preferred

Calibration: STANDARDS § Calibration actually involves comparison to a known standard. § There are three types used for calibrating air sampling pumps: primary standards, intermediate standards, and secondary standards.

Calibration: STANDARDS § Primary standards are the most accurate. § Intermediate and secondary calibration standards for flow are calibrated against primary standards. § The most fundamental calibration techniques for most practicing industrial hygienists is use of primary and secondary devices to calibrate air sampling pumps. Only these two major types of calibration devices will be described.

Calibration: “BUBBLE-TUBE” § The frictionless bubble-tube (or soap-film flowmeter) is an example of a major primary standard commonly used for industrial hygiene applications. § The bubble-tube consists of an inverted transparent volumetric burette or glass burette-like column wetted on the interior with distilled water and soap solution.

“Bubble-Tube” § An air sampling pump is connected to the bubble-tube via a length of flexible hose. § The volume displacement of air per unit time, or flow rate, can be determined by measuring the time required for a bubble/soap film contained in the tube to pass between two scale markings that enclose a known volume. § The flow rate (Q, L/min) is determined by dividing the volume traversed by the bubble (V, cc) in the bubble-tube by the time measured (T, sec) for the bubble to travel across the specific volume. Fig. 4. 4: Calibration train for total particulate composed of (a) high-flow pump connected with flexible hose to (b) a 37 -mm PVC filter in three-stage cassette in line with (c) frictionless bubble-tube

“Bubble-Tube” Flow Rate: http: //www. sepscience. com/Information/Archive/GC-Solutions/1636 -/ GC-Solutions-34 -Split-Sample-Introduction---Part-2 -Measuring-Flows-Liner-Choice

Bubble Tube http: //www. skcinc. com/prod/311 -100. asp

Important Equations: § FLOW RATE § AVERAGE FLOW RATE (Qavg): Based on the average of pre- and post-sampling flow rates

Important Equations: § AIR VOLUME SAMPLED (m 3) § CONCENTRATION

TEMPERATURE AND PRESSURE § Recall: Ideal Gas Law: § Air temp and atmospheric pressure should be measured during calibration procedures. § Permits correction of actual flow rate (Qact) to standard flow rate (Qstd), where standard or normal temp and pressure equal 25°C (298 K) and 760 mm. Hg (1 atm), respectively

Temperature and Pressure: Adjustment

Electronic Bubble-Tube § Electronic bubble-tube flow meters work based on the same principle as the manual meters described previously, however they have an electronic sensor that automatically determines the time for the bubble to travel for a given volume and automatically measures flow rate. § These devices must be factory calibrated periodically. http: //www. mesalabs. com/tag/defender-series/

Manual Bubble-Tube Rotameter Electronic Bubble-Tube

Secondary Standard: ROTAMETER § A rotameter is a major secondary standard for calibrating air sampling pumps § The device consists of a tapered, precision bored tube, made of transparent glass or plastic, with a solid float inside § Air flow enters the bottom of the tube and carries the float upward until a level is reached where the force of the air is offset by the weight of the float. § The height of the float from the bottom of the tube represents the air flow rate. The float should be read at its highest, widest point.

ROTAMETERS § Calibrated by comparison with a primary calibrating device § Ex: an active flow air sampling pump, rotameter, and bubble-tube are connected in-line using flexible hosing. § Flow-rate readings measured using the bubble-tube and corresponding rotameter readings for five different flow settings are recorded § Data can be plotted using a linear graph showing rotameter readings v. bubble-tube flow rate readings. § Corresponding flow rates for various rotameter readings can later be extrapolated from the curve http: //www. skcinc. com/prod/320 -100. asp

Rotameter Calibration Chart 0 9 22 31 42 50 63 Bubble-Tube Flow Rate (L/min) 0 0. 5 1 1. 5 2 2. 5 3 70 Rotameter Reading 60 50 40 30 20 10 0 0 0, 5 1 1, 5 2 2, 5 Bubble-Tube Flow Rate (L/min) 3

ROTAMETERS § A rotameter should always be calibrated under the same conditions of pressure, temperature, and density as it is to be used. § Once calibrated, the rotameter can be used directly to calibrate air sampling pumps. This is especially useful in the field due to simplicity.

Example calculation 1: § A multi-flow air sampling pump was calibrated using a mechanical frictionless bubble-tube. What was the average flow rate (Q) in L/min if three trials were run resulting in 25. 5 sec (T 1), 25. 2 sec (T 2), and 25. 9 sec (T 3) for the bubble to traverse a volume of 1000 cc?

Answer 1: § 2. 35 L/min § See next slide for calculations

Solution 1:

Example calculation 2: § A rotameter was calibrated using a frictionless bubble-tube as a primary standard. Data are shown below. What would the calibration curve look like? What is the flow rate (L/min) if the rotameter reading is 35? Rotameter Reading 0 12 23 34 47 58 71 Bubble-Tube Flow Rate (L/min) 0 0. 5 1 1. 5 2 2. 5 3

Rotameter Calibration Chart Ex. 2 Rotameter Reading 80 70 60 50 40 30 20 10 0 0 0, 5 1 1, 5 2 2, 5 Bubble-Tube Flow Rate (LPM) 3 3, 5 Flow rate is approximately 1. 5 LPM

*SPECIAL NOTE: § Calibration also refers to the use of “Reference gases” or other “Standards” to calibrate instantaneous monitoring instruments. § Examples: § Combustible Gas/Vapor & Oxygen Gas Meters § Flame Ionization Detectors and Photoionization Detectors

Calibration Reference Gas

Module # Major Instantaneous Monitoring Instruments: Gases and Vapors Exposure Science Monitoring Techniques Michael Bisesi, Ph. D, REHS, CIH Senior Assoc. Dean, Academic Affairs Director, Center for Public Health Practice Assoc. Professor, Environmental Health Sciences

Module: Major Instantaneous Monitoring Instruments: Gases and Vapors References: § Bisesi, M. (2003, 2 nd ed. ). Bisesi & Kohn’s Industrial Hygiene Evaluation Methods. CRC press/Taylor & Francis Publishers. Boca Raton, FL. § CDC/NIOSH Manual of Analytical Methods. http: //www. cdc. gov/niosh/docs/2003 -154/

Major Instantaneous Monitoring Instruments § Combined Combustible Gas/Vapor and Oxygen Gas Meter § [Combustible Gas or Vapor] %of LFL or %LFL § [Oxygen gas] % § Piston or Bellows Pumps with Detector Tubes § [Inorganic gases] ppm § [Organic gases & vapors] ppm *LFL = lower flammable limit

Gases & Vapors (cont. ) § Flame Ionization Detector Meters § [Ionizable Organic Vapors] ppm § Photoionization Meters § [Ionizable Organic Vapors] ppm § Infrared Meters § [Organic Vapors] ppm § [Inorganic Gases] ppm

Multi-Gas Detector

Dual FID/PID Analyzer