# Presentation: 580512

## Calibration:  Ensuring Precision and AccuracySampling for Silica and Heavy Metals

- Aaron L. Sussell, PhD. MPH, CIH. 	Catherine Beaucham, M.P.H
- Health Scientist			 	 Public Health Specialist
- Certified Industrial Hygienist 	  	Industrial Hygienist

- Calibración:  Asegurar precisión y exactitud.*Muestreo para la Sílice y metales pesados*

## Calibration:  Ensuring Precision and Accuracy Calibración:  Asegurar precisión y exactitud

- Objectives
- To understand why we need to calibrate sampling equipment
- To identify the importance of precision and accuracy in industrial hygiene sampling
- To explain primary and secondary calibration standards, and the proper use of each type

**Objetivos**
**Entender porque necesitamos calibrar el equipo de muestreo.**
**Identificar la importancia de precisión y exactitud en muestreo de higiene industrial**
**Explicar la diferencia entre estándares de calibración  primarios y secundarios, y el uso apropiado de cada tipo**.

## Why calibrate ? ¿Por que calibrar?

- To ensure exposure measurements are accurate
**Asegurar medidas de exposición sean exactos**
- To have legally and scientifically defensible data
**Tener datos legalmente y científicamente defendibles**

**Notes:**
Measurements in IH are only as good as the calibration upon which they are based.  Measurements that are made with an instrument that is not properly calibrated may lead to false conclusions about the hazard level in the workplace.  Calibration is done by adjusting the instrument until it properly measures to a known standard within acceptable limits.  It is done before and after each use.

## Definitions/ Definiciones

- Accuracy:  The difference between a measurement and the true value**Exactitud:  La diferencia entre una medida y el valor verdadero**
- Precision:  determined by random errors
-     **Precisión:  determinado por errores al aleatorios**
- Bias:  determined by systematic errors
-     **Prejuicio: determinado por errores sistemáticos**

**Notes:**
What does accuracy mean?
Accuracy is the difference between a measurement and the true value.  It is not possible to make a measurement with no error and thus we can never know the true value, we can only estimate it.  Every measurement has some degree of error.  Precision and bias are aspects of measurements that are determined by different types of measurement error.  Precision is determined by the magnitude of random errors and bias by systematic errors.  

## Use of Standards / Uso del Estándares

- In chemistry and physics measurements can sometimes be compared to a standard value
**En la química y física a veces se puede comparar las medidas con un valor estándar****.**
- The standard is made to be a certain value and represents the “true value”.
**Se hace el estándar a ser un valor especifico, y representa el “valor verdadero.”**

**Notes:**
Se hace el estándar a ser un valor específico, y representa el “valor verdadero.”

## Precision and Bias:  ExamplesLa precision y la exactitude / Ejemplos

- Preciso e exacto

- Impreciso y inexacto

- Impreciso y exacto

- True Value

**Notes:**
A good measurement is precise and unbiased.  Precision means that repeated measurements give more or less the same value.  Unbiased means that the measurements are randomly distributed around the true value, not in one direction or another.  

Random Errors:  Affect Precision-Random/unpredictable variations in the instrument, such as flow rate variations.

Systematic Errors:  Affect Bias-Non-random characteristics of the sampling system, such as if all the air sampling filter cassettes have some leakage.

## Sources of Error:  Air SamplingFuentes de error:  Muestreo de aire

- Pump flow rate not correct
- Filter “Bypass” Air leakage with plastic cassettes
- Calibration errors

**El  flujo de la bomba no es correcta.**
**Fuga de aire con los casetes plásticos **
**Errores con la calibración**

**Notes:**
What are common sources of error in air sampling?
In air sampling the results are often expressed as mass per unit volume.  There is a possibility for error in measurement of either quantity.  The volume of air collected by a pump depends on the flow rate and the sampling time. It is quite easy to accurately measure time, so when collecting samples with air sampling pumps, the overall sample result is usually only as precise or accurate as your measurement of the pump flow rate. This is also something the industrial hygienist has total control of.  If a pump is correctly calibrated and maintained, the flow rate variation during the work shift ideally should be within ± 5%. 
Another common type of error is bypass leakage due to improperly assembled filter cassettes. Large errors can result because a good part of the air contaminant of interest will be not be collected, but will “bypass” (flow around, rather than through) the filter or other sample media.  Calibration errors (failure to calibrate correctly) can result in large errors in the volume measurement and the sample results.  

## Sources of Error:  Air SamplingFuentes de error:  Muestreo de aire

- Laboratory instrument signal “noise”
- Standards not correct

**Errores de medida en el laboratorio**
**Estándares no correctos.**

**Notes:**
What are common sources of error in air sampling?
The other common source of error for air sampling is in the measurement of mass (or concentration) in the laboratory analysis of the sample.  There is always some amount of random error in the analytical method, and there could also be systematic error in the laboratory due to persistent contamination problems, instrument problems, incorrect calibration of lab equipment, etc.

## What can an IH do to ensure that measurements are accurate when sampling?¿Cuando esta realizando muestras, que puede hacer un IH para asegurar la exactitud de las muestras?

## Why is it important to have a sampling method that is - Precise? and Accurate?¿Por qué es importante tener un método de muestreo que es preciso e exacto?

## Measuring air flow rateMedir la proporción de flujo de aire

- Primary Standards:  usually directly measure air flow (time) in an enclosure with known volume.
**Estándares primarios:  ****Mida directamente el flujo de aire (tiempo) en un envase con el volumen sabido**
- Secondary Standards: instruments and flow rate meters that measure flow indirectly--must be calibrated with primary standards.
**Estándares secundarios: ****instrumentos y metros de la proporción de flujo que midan indirectamente, deben ser calibrados con estándares primarios**

**Notes:**
When we calibrate an air sampling pump we are measuring flow rate.  The flow rate is the volume of air collected per unit time, usually expressed in liters/minute.

## Calibrator ClassificationsClasificaciones del calibradores

- Primary Standards Estándares primarios
- Accuracy is considered to be ±1% or better.
**Exactitud es ±1% o mejor**
- Manual calibration vs. electronic calibration.
**Calibración por mano o electrónico**

**Notes:**
Select VIDEO of Bubble Burette.

What are the most common flow rate calibration devices used in the field?
The most common devices are bubble buret, electronic bubble flow meter, and precision rotameters.
One the simplest primary standards for measuring flow rate is the soap film bubble burette.  The equipment is relatively simple and inexpensive.  However, it is not very portable or rugged.  Also, the measurements are completely manual, and so calibration takes longer than other methods (the movement of the soap bubble in the burette must be manually started and timed with a stopwatch).  The electronic bubble meter uses the same principle of operation, but the instrument automatically times the movement of the soap bubble.  The electronic meter is much faster, and in most cases, more accurate.  However, the initial cost of the instrument is much greater.

## Calibrator ClassificationsClasificaciones del calibradores

- Secondary Standards
**	****Estándares secundarios**
- Accuracy is considered to be ±5% or better if calibrated
**Exactitud es ±5% o mejor, si calibrada.**
- Must be calibrated against a primary standard for each use.
**Tiene que calibrarlo contra estándar primario para cada uso.**
- Rotameters are affected by barometric pressure (or altitude) and must be calibrated at field location.
**“****Rotameters”estan afectadas por la presión barométrica (y/o la altura) y tiene que hacer la calibración en el lugar donde va a tomar las muestras.**

**Notes:**
The most commonly used secondary standard is the rotameter.  The precision rotameter consists of a vertically mounted internally tapered tube, with a float inside so that it is free to move up and down.

All rotometers need to be periodically calibrated against a primary standard.  

Pump rotometers are frequently inaccurate.  

## More about rotametersMas sobre rotameters

- Built-in pump rotameters
- _NOT for calibration _
- They are only approximate
- Useful to verify flow during sampling

**Rotameters en la bomba**
_**No lo usa para calibración**_
**Solo para aproximación**
**Son útiles para verificación de flujo durante muestreo**

**Notes:**
Why don’t we just use the built-in rotameters on sampling pumps for calibration?

The built-in rotameters on pumps are not accurate enough.  They are provided as a convenience to the user--you can use them to see if the pump is running and what the approximate flow rate is.
On the other hand, precision rotameters can be quite accurate if they are first calibrated with a primary standard such as a bubble flow meter.  However, the factory stamped-in flow rate marks on some precision rotameters may not be correct due to variations in the ball weight and tube size.  For example, at the 1-liter per minute (Lpm) mark a rotameter may actually be measuring 1.2 Lpm.  It is important that the actual flow rates be written on the side of the rotameter (put marks and labels on a piece of tape) when the instrument is calibrated. built-in rotameters on the sampling pumps are not precision rotameters--they will not provide accurate readings for calibration.  

## More about rotametersMas sobre rotameters

- Precision rotameters
- can be accurate (± 3%)
- must be calibrated with primary standard at location
- factory marks may not be accurate

**Rotameters de precisión**
**Pueden ser exactos (****± 3%)**
**Tiene que calibrarlos contra un estándar primario en el campo**
**Las marcas del fabricante no siempre son exactos**

**Notes:**
Why don’t we just use the built-in rotameters on sampling pumps for calibration?

The built-in rotameters on pumps are not accurate enough.  They are provided as a convenience to the user--you can use them to see if the pump is running and what the approximate flow rate is.
On the other hand, precision rotameters can be quite accurate if they are first calibrated with a primary standard such as a bubble flow meter.  However, the factory stamped-in flow rate marks on some precision rotameters may not be correct due to variations in the ball weight and tube size.  For example, at the 1-liter per minute (Lpm) mark a rotameter may actually be measuring 1.2 Lpm.  It is important that the actual flow rates be written on the side of the rotameter (put marks and labels on a piece of tape) when the instrument is calibrated. built-in rotameters on the sampling pumps are not precision rotameters--they will not provide accurate readings for calibration.  

## Measuring air flow with rotameterMedir el flujo de aire con un rotameter

- Not  for calibration
**No lo utiliza para calibración**

- For calibration – if checked with primary standard at location
**Lo utiliza para calibración-si verificar lo contra un primario en campo**

## What is the difference between primary and secondary standards for measuring air flow rate?¿Cual es la diferencia entre el estándar primario y el estándar secundario con el medir del proporción de flujo?

## Pump Calibration ProcedureProcedimiento de calibrar la bomba

- Select appropriate pump(s) and sampling media.
- 2. Turn on pump(s) and allow to run for at least 5 minutes.

**Seleccionar la bomba y filtro apropiada.**
**2.  Prender la bomba y dejarlo por lo menos 5 minutos.**

## Pump Calibration ProcedureProcedimiento de calibrar la bomba

- 3. Record date, time, pump type and number, calibration device and number, and type of collection media.
- 4. Start calibration device
- 5. Attach media to pump with Tygon tubing.

**3.  Marcar la fecha, hora, el tipo y numero de bomba, equipo de calibración, y numero y tipo de filtro.**
**4. Prender el equipo de calibración.**
**Fijar el filtro a la bomba con un tubo tipo “Tygon.”**

## Pump Calibration ProcedureProcedimiento de calibrar la bomba

- 6.  Attach the other side of the media to the calibrator with Tygon tubing.
- 7. With the pump running start the calibration.  Measure the flow rate with 3-5 samples.  Record the average flow.
- 8. Check the flow rate after air sampling, to verify flow has not drifted > 5%.

**6. ****	****Fijar otro lado del filtro al calibrador con tubo tipo “Tygon”**
**7. Con la bomba prendida, empezar la calibración.  Medir la tasa de flujo con 3-5 muestras.  Registra el promedio.**
**8. Verificar la proporción de flujo después del muestreo para verificar el flujo no ha cambiado > 5%**

**Notes:**
Remember:  Standard industrial hygiene practice is to calibrate with representative media in-line, before and after each sampling period, and under the temperature and pressure conditions of the sampling location.  

## Industrial Hygiene Virtual Lab

**Notes:**
Click on the photograph to perform pump calibrations!

## Calibration RecordsRegistro de Calibración

**Notes:**
You should maintain detailed records of the calibration of your equipment.  

## Closed Cassette

- _[Video Clip](file:///lab1a_closedCassette.mov)_

## Cyclone Filter

- _[Video Clip](file:///lab1a_cyclone.mov)_

## Bell jar-Calibration 

- _[Video Clip](file:///1a_belljar.mov)_

## Calibration ExampleEjemplo con calibración

- Using the bubble burette that contains 1000mL, your sample runs 43.8 seconds from 0mL to 1000mL.  How many liters per minute is your pump running?
**Usando un envase que contiene 1000mL, dura 43.8 segundos llegar desde 0mL hasta 1000mL.  Cuantos litros por minuto esta corriendo su bomba?**

**Notes:**
1.)  Convert seconds into minutes:  43.8 seconds/60 seconds per minute=0.73 minutes
2.)  Convert mililiters into liters: 1000mL=1L
3.)  Determine the flow rate in liters per minute:  1 L/ 0.73 min=1.4 LPM

## Field Sampling SheetsHoja de muestreo en campo

## NIOSH Analytical MethodsMétodos Analíticos

- _[Silica, Crystalline by IR-7602](file:///7602.pdf)_
- _[Metodo](file:///MA_057_A04.pdf)__[ de ](file:///MA_057_A04.pdf)__[analisis](file:///MA_057_A04.pdf)__[ ](file:///MA_057_A04.pdf)_Silice cristalina
- _[Heavy Metals –by ICP-7300](file:///7300.pdf)_
- _[Metodo](file:///ntp_110.pdf)__[ de ](file:///ntp_110.pdf)__[analisis](file:///ntp_110.pdf)__[ ](file:///ntp_110.pdf)_Metales Pesados

## References/Referencias

- Industrial Hygiene Virtual Laboratory. [CD-ROM].  Athens, (OH): Timothy J. Ryan, CIH, CSP.; 2002
- Industrial Hygiene Manual. [online]. 2005.  Ohio Bureau of Workers’ Compensation, Div. of Safety and Hygiene.  Email: library@bwc.state.oh.us
- Methods Chapters A-R.  NIOSH Manual of Analytical Methods.  Cincinnati, OH: Centers for Diseae Control and Prevention.
- http://www.cdc.gov/niosh/nmam/chaps.html

## ¿Preguntas?

- The findings and conclusions in this presentation are those of the authors, and not necessarily those of the National Institute for Occupational Safety and Health. The content in this presentation has not been formally disseminated by the National Institute for Occupational Safety and Health.

- Gracias para su atención.