Application Note

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2 Fluke Corporation Fundamental IAQ/HVAC measurements with the Fluke 975 AirMeter™

Carbon Monoxide

Fundamentals

Carbon Monoxide (CO) is a prod-

uct of the incomplete oxidation

of carbon during combustion and

is undesirable at any levels in

an occupied space. Carbon mon-

oxide is colorless, tasteless and

odorless. The longer the expo-

sure and the higher the concen-

tration, the more CO is retained

by the blood, leaving less and

less room for oxygen. At lower

levels of exposure, CO causes

flu-like symptoms such as head-

aches, dizziness, disorientation,

nausea and fatigue. At higher

levels of exposure, CO is deadly.

If a healthy person is exposed

to 200 ppm CO over a one hour

period the affects would be

barely perceptible, cause illness

after three hours, and death after

six hours.

The U.S. National Ambient Air

Quality Standards for carbon

monoxide levels in outdoor air

are 9 ppm for 8 hours, and 35

ppm for 1 hour. ANSI/ASHRAE

Ventilation standard 62.1-2004

adopts these values for indoor

air. These are believed to be

acceptable levels of exposure

for persons with respiratory or

heart conditions. OSHA limits

exposure for healthy persons in

a workplace to 50 ppm CO for an

eight hour period. CO levels in

an inadequately ventilated ware-

house that uses LP gas fueled

forklifts can easily rise above

50 ppm.

The NFGC limits CO in a furnace,

boiler or water heater to 400

ppm in an air free sample, which

means actual CO readings in the

vent would be 250 – 300 ppm,

although these levels in a mod-

ern heating appliance would be

cause for alarm. CO levels in a

central heating or water heating

appliance vent should be 50 ppm

CO or less. CO levels in a kitchen

using a gas oven can be 35 ppm.

Unvented space heaters pose a

significant threat when there is

insufficient ventilation. Complete

combustion takes oxygen from

the occupied space and results in

vent products that consist of car-

bon dioxide and water vapor. As

this process continues in a poorly

vented space, oxygen is depleted

and carbon dioxide accumu-

lates. This deprives the burner

of sufficient oxygen resulting in

incomplete combustion and the

elevated production of CO.

Possible sources of carbon mon-

oxide include the incomplete

combustion of any organic com-

pound including wood, coal or

charcoal, fuel oil, natural or LP

gas, gasoline or diesel fuel, kero-

sene, cigarettes, and so forth.

How the 975 measures it

The 975 AirMeter

™

offers several

methods for tracking sources

of CO. The meter can be set for

“MIN MAX” allowing the user to

switch between live, maximum,

minimum and average CO read-

ings. The user can walk from

space to space to track the high-

est levels of CO. If CO readings

are higher at an air diffuser,

then the HVAC system blower is

circulating the CO from another

location, such as the heating

plant. In that case, you would

turn the thermostat down and

set the system blower to “ON”.

If the level of CO from the dif-

fuser didn’t diminish, the CO is

from another source. Check areas

where combustion is occurring to

find malfunctioning equipment,

as well as occupied spaces adja-

cent to parking garages or ware-

houses. Those exhaust systems

may not be keeping those spaces

at a lower differential pressure.

When data logging or trending is

needed, the 975 AirMeter

™

can

record four samples per minute

over a four day period. The log-

ging session can be downloaded

to a computer for analysis and

FlukeView

Forms software can

create a graph charting peak

occurrences.

Carbon Dioxide

Fundamentals

Carbon dioxide is a normal prod-

uct of respiration and complete

combustion of organic compounds.

It is used extensively for many

purposes including carbonated

beverages. Carbon dioxide is an

asphyxiant at high levels and

50,000 ppm CO

is considered an

immediate threat to life. Normal

levels of outdoor environmental

carbon dioxide in the atmosphere

range from 300 ppm to 600 ppm

depending on location and back-

ground activity (rush hour in the

city). OSHA sets an upper limit

of 5,000 ppm CO

over an eight

hour day, or 10,000 ppm CO

over one hour. For typical fully

occupied spaces requiring 15 cfm

per person, ANSI/ASHRAE Ventila-

tion standard 62.1-2004 requires

sufficient ventilation to maintain

700 ppm CO

above outside CO

levels. This CO

level is selected

to control odors and contaminant

levels and is much lower than CO

levels that would begin to affect

human activities.

Measuring CO around a gas water heater.