Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 404

ExcessAir
Theoretical Air

=

×100

%ExcessAir (15.10)

ExcessAir
TotalAir

×100

%ExcessAir = (15.11)

− ExcessAir

Theoretical air is that amount required to stoichiometrically convert all combustible species
(mainly carbon, hydrogen, sulfur) to complete normal products of combustion (CO 2 , H 2 O, and SO 2 ).
These relationships are stated as mole ratios of air, which equal volume ratios. In Method 3B,
USEPA (2003b) provides the following explanation for determining percent excess air.

15.5.5.1 Example USEPA Calculation for Percent Excess Air
Determine the percentage of the gas that is N 2 by subtracting the sum of the percent CO 2 , percent
CO, and percent O 2 from 100%. Calculate the percent excess by substituting the appropriate values
of percent O 2 , CO, and N 2 into Equation 15.12.

%O 0.5%CO
0.264%N

−

×100

2

%ExcessAir = (15.12)

− ( O − 0.5%CO )

2 2

Equation 15.12 assumes that ambient air is used as the source of O 2 and that the fuel does not
contain appreciable amounts of N 2 (as do coke oven or blast furnace gases). For those cases when
appreciable amounts of N 2 are present (coal, oil, and natural gas do not contain appreciable amounts
of N 2 ) or when oxygen enrichment is used, alternative methods are required.

15.5.6 a tmospheriC s tandards
To perform various indoor and outdoor air pollution calculations, knowledge of the following atmo-
spheric standards is important.

15.5.6.1 Standard Temperature and Pressure
Standard temperature and pressure (STP) is the designation given to an ambient condition in which
the barometric pressure and the ambient temperature are as follows:

Barometric pressure

1 atm, 760 mmHg, 14.70 psia (pressure per square inch absolute), 0.00 psig (pressure per
square inch gauge), 1013.25 millibars, or 760 Torr

and

Ambient temperature

0°C, 32°F, 273.16 K, or 491.67°R

15.5.6.2 Normal Temperature and Pressure
Normal temperature and pressure (NTP) is the designation given to an ambient condition in which
the barometric pressure and the ambient temperature are as follows:

Barometric pressure

1 atm, 760 mmHg, 14.70 psia, 0.00 psig, 1013.25 millibars, or 760 Torr

and
Ambient temperature

25°C, 77°F, 298.16 K, or 576.67°R