You are a consultant for a major construction company and have been hired to determine worker exposure to silica dust. You initially calibrate a personal sampling pump at a flow rate of $2\mathrm{.}75lpm.$ After completing a full shift sample $(8-$hr$),$ you determined during post$-$calibration that the flow rate had dropped to $2\mathrm{.}65lpm.$ The laboratory reports that filter contained $1\mathrm{.}0mg$ of crystalline silica.

a$)$ If you wish to be most protective $($assume a worst case exposure estimate$),$ which flow rate would you choose?

b$)$ If you were working for OSHA and you were required to give the employer the benefit of the doubt $($assume the best case exposure estimate$),$ which flow rate would you choose?

c$)$ Calculate the $8hr.$ TWAs using both flow rates and calculate the difference between two different concentrations.

Explain why it would be inappropriate to use a non$-$calibrated precision rotameter to calibrate a personal sampling pump.

Some personal sampling pumps come with built$-$in rotameters.

a$)$ How useful are these rotameters in providing the "true" flow rates of the pump?

b$)$ What is the main purpose of the pump rotameters?

Why is it necessary to have a filter cassette or other sampling device connected to the sampling pump during calibration procedures?

List the main advantage and the main disadvantage of using a secondary calibration unit like a rotameter to calibrate sampling pumps?

If it takes $10$ seconds for a bubble to travel from $0$ to $500ml,$ what is the flow rate in lpm$?$

You were asked to calibrate a precision rotameter using a bubble burette.

a$)$ Draw a calibration curve using the following results:

$\backslash$table$[[\backslash$table$[[$Bubble burette$],[$flow rate in lpm$]],\backslash$table$[[$Precision rotameter$],[$Reading in lpm$]]],[1\mathrm{.}0,1\mathrm{.}4],[2\mathrm{.}0,3\mathrm{.}0],[3\mathrm{.}0,4\mathrm{.}9],[4\mathrm{.}0,6\mathrm{.}4]]$

b$)$ When a personal sampling pump was calibrated using the precision rotameter, the rotameter read $3\mathrm{.}8lpm.$ What is the estimated flow rate in $lpm$ using the above calibration curve?