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The Advisor Genius: Calculating the Wood Equation
BEFORE YOU BEGIN
The breakthrough calculator is available in two versions:
- A downloadable Microsoft Windows program NIOSH Publication No. 2010-124C. This program is similar to the Advisor Genius, but has been updated and includes corrections for humidity.
- An on-line Advisor Genius developed in 1998, described below.
- The Advisor Genius will estimate the contaminant breakthrough time for an activated carbon respirator cartridge using physical and environmental parameters specific to the contaminant and the workplace. It only applies to contaminants that are liquids at the workplace temperature.
- The Advisor Genius already knows the physical parameters for 120 chemical compounds. If your contaminant is not one of these 120, you will be asked for the following:
The Advisor Genius will ask you for the following information. Be prepared and remember to enter the information that best describes your workplace and worst-case working conditions.
- Chemical name
- Molecular weight
- Liquid density in units of grams per cubic centimeter at the workplace temperature
- Vapor pressure of the contaminant in units of torr at the workplace temperature
- Molar polarization in units of cubic centimeters per mole
The advisor will use your selections to calculate a service life based on theories developed by Gerry Wood.
- Number of cartridges used by the respirator
- Weight of sorbent in each cartridge in grams
- The carbon micropore volume in cubic centimeters per gram. If you cannot obtain this number from the manufacturer, you can assume a standard value of 0.4.
- Bulk density of the packed bed in units of grams per cubic centimeter. You can calculate this by disassembling a respirator cartridge and determining the total volume of the bed then dividing this number into the sorbent weight.
- The maximum temperature expected in the workplace in degrees.
- The maximum humidity expected in the workplace. The calculator assumes that the maximum humidity will be less than 65%. For higher humidities you must apply a safety factor to the calculated breakthrough time.
- The maximum concentration of contaminants in the workplace in units of parts per million or milligrams per cubic meter.
- The workrate (volumetric flow rate) in units of liters per minute (LPM). This reflects the type of work being performed, with office work giving typical workrates of about 20 LPM and heavy work giving workrates in excess of 60 LPM.
Remember that there are many variables which can influence respirator service. Therefore, the result from this advisor does not guarantee compliance with OSHA regulations and should only be used as initial guidance.