Using Carbon Dioxide as a Tracer Gas to Measure Air Change Rate ...

Using Carbon Dioxide as a Tracer 

Gas to Measure Air Change Rate in a 

Single Zone 

C. Simmons, F. Boelter, G. Crawford, Boelter & Yates, 

Inc., Park Ridge, IL 

Presented by: 

Catherine E. Simmons, CIH 

Boelter & Yates, Inc. 2004

Situation 

Ventilation information was needed to 

perform a retrospective exposure 

assessment. 

Procedure was needed to determine the 

ventilation rate in air changes per hour 

(ACH) for representative boiler rooms and 

an isolation test chamber. 


Boiler Room Ventilation 

Research 

Published Information on Boiler Room Air 

Change Rates 

ASHRAE, BOCA and NFPA reviewed for 

ventilation requirements in ACH 

Ventilation Models Using Tracer Gas 

Published Ventilation Models using Tracer Gas 

Standard Test Method for Determining Air 

Change in a Single Zone by Means of a Tracer 

Gas Dilution – ASTM E 741 – 00 


Problem 

Existing methods allow for the use of a variety of tracer 

gases to be used. 

Each has advantages and disadvantages. 

Selected method 

highly portable 

easily measured 

non-toxic or very low toxicity 

inexpensive 

Tracer gas acceptable to school district personnel. 


Research 

Standard Test Method for Determining Air Change in a 

Single Zone by Means of a Tracer Gas Dilution – ASTM E 

741 – 00 

Tracer gases (examples) 

CO 2 – PEL 5000 ppm 

SF 6 – PEL 1000 ppm 

CO – PEL 50 ppm 

Selection of test method 

Concentration Decay 

Constant Injection 

Constant Concentration 


Resolution 

Selection of tracer gas 

Carbon dioxide 

Relatively high PEL 

Inexpensive 

Easy to obtain and measure 

Acceptable to School personnel 

Selection of method 

Concentration Decay Test Method 

Measures the decay rate of carbon dioxide over 

time to calculate the air exchange rate. 

Regression Analysis 

InC(t) = -At + C(0) 

 


Sample Time 

Air Change Rate (1/hr) 

0.25 

0.5 

1 

2 

4 

Boelter & Yates, Inc. 2004 

Minimum Duration (hour) 

4 

2 

1 

.5 

.25 

Minimum sample duration based on 10% uncertainty at the 95% 

confidence level in the detection of air change rate, a tracer gas 

concentration measurement precision error of 5% of reading and 

various air change rate. Using the regression method reduces the 

minimum test duration due to more than 2 data points.

Boiler Room Ventilation 

Testing Using Tracer Gas 

Representative Boiler Rooms 

Elementary School - IN 

Elementary School - IL 

Middle School - IL 


Gas Injection and Distribution 


Direct Reading Equipment 

TSI Q-Trak 

Log Data 


School 

Indiana 

• 5500 ft 3 Boiler Room 

• Volume of gas needed 

• Calculated based on room 

size and target 

concentration of 4000 ppm 

V tracer = C target X V zone 

• 2 boilers 

– Input BTU/hr. - 117,000 

– Input BTU/hr. – 156,000 

• Both boilers operating 

during the testing 

• No mechanical ventilation 


Carbon Dioxide 

Concentration in Parts Per 

Million (PPM) 

4500 

4000 

3500 

3000 

2500 

2000 

1500 

1000 

500 

0 

Average CO2 Concentration vs Time 

Indiana Boiler Room - 2 Boilers Operating 

March 26, 2003 

1 7 13 19 25 31 37 43 49 55 61 67 73 

Time in Minutes 

Trial 1 – 5.2 ACH Trial 2 – 5.3 ACH 

Average 5.2 ACH 


Trial 1 - Average 

CO2 Concentration 

(PPM) 5.2 Air 

Changes Per Hour 

Trial 2 - Average 

CO2 Concentration 

(PPM) 5.3 Air 

Changes Per Hour

Elementary School 

Illinois 

• Measured Volume – 

24,322 ft3 . 

• 2 Boilers 

• Ventilation tracer 

gas testing 

conducted with 

boilers on and off. 


4000 

3000 

2000 

1000 

0 

Ventilation Rate - Boilers Off 

1.8 Air Changes Per Hour 

March 27, 2003 

0 18.75 37.5 56.25 


Trial 1 

Boilers Off - 1.8 ACH 

Elementary School 


Concentration 

(ppm) 


Concentration 

(ppm) 

5000 

4000 

3000 

2000 

1000 

0 



March 27, 2003 

0 

2.25 

4.5 

6.75 

9 

11.3 

13.5 

15.8 

18 

20.3 

22.5 

24.8 

27 

29.3 

31.5 


Boilers On 

Trial 2 – 3.5 ACH 

Trial 3 – 3.9 ACH 

Average 3.7 ACH 

Trial 2 - Average Carbon 

Dioxide Concentrations 

with 2 Boilers Operating 

Trial 3 - Average Carbon 

Dioxide Concentrations 

with 2 Boilers Operating

Middle School 

Illinois 

16,372 ft 3 

Boiler 

Room 

2 Identical 

Boilers 


5000 

4000 

3000 

2000 

1000 

0 

Average Carbon Dioxide Concentration (ppm) vs 

Time 

Middle School 

March 21, 2003 

0 25 50 


75 

Boilers Off 

1.2 ACH 

Middle School 


Concentration (ppm) 


Concentration (PPM) 



Boiler Room - 2 Boilers 

March 31, 2003 

5000 

4000 

3000 

2000 

1000 

0 

1 112131415161718191 


Boilers On 

Trial 2 - 4.4 ACH 

Trial 3 - 5.3 ACH 

Average – 4.9 ACH 

Boilers On (1 boiler on part 

time): Trial 2 - Average CO2 

Concentration 4.4 Air 

Changes Per Hour, 

GlenCrest School March 31, 

2003 

Boilers On: Trial 3 - Average 

CO2 Concentration 5.3 Air 

Changes Per Hour, 

GlenCrest School March 31, 

2003

Measured Range of Boiler Room 

Ventilation 

Summary 

Boilers Off 

Range: 1.2 to 1.8 ACH 

Boilers On 

Range: 3.7 to 4.9 ACH 


Isolation Test Chamber 

• Approximately 20’ x 20’ x 9’ 

(3600 ft3 ) 

• Wood Frame 

• Polyethylene sheeting on 

walls and floors 


• 2 viewing windows 

• Entrance airlock 

• Decontamination Shower (if 

needed) 

• HEPA filtered exhaust 

machines for ventilation

HEPA Filtered Exhaust Machines 

for Chamber Ventilation System 

Note: Using various configurations, both machines operated 

as exhaust (tubing was attached to machines to exhaust 

outside the building). 


Installation and Measurement of 

Ventilation System 

Various configurations to achieve 

approximately 1, 3, 5 and 10 ACH 

Carbon dioxide tracer gas used to 

measure ventilation rate. 

Each rate tested twice to assure 

repeatability. 

Final ventilation rates were: 1.2, 2.9, 5.7, 

10.7 ACH. 



Concentration (ppm) 

6000 

5000 

4000 

3000 

2000 

1000 

Carbon Dioxide Concentration (ppm) vs Time 

B & Y Test Chamber 

5.7 Air Changes Per Hour 

April 29, 2003 

0 

16:28 

16:30 

16:32 

16:34 

16:36 

16:38 

16:40 

Time 



16:42 

16:44 


Average 5.7 

16:46 

16:48 

16:50 

Trial 1 - high 

Trial 1 - low 

Trial 2 - high 

Trial 2 - low

Conclusions 

Ventilation rates for representative boiler 

rooms were between 1 and 5 ACH. 

Using carbon dioxide as a tracer gas and 

following ASTM E 741 – 00, Standard Test 

Method for Determining Air Change in a 

Single Zone by Means of a Tracer Gas 

Dilution met the objectives and goals of the 

project. 


Benefits 

Carbon Dioxide as a tracer gas 

Inexpensive, reliable procedure for IH’s to determine 

ventilation rates. 

Measuring Equipment is readily available 

The method provides an additional tool for 

industrial hygienists to better characterize 

workplace conditions during the initial stages of 

an exposure assessment. 

Ventilation information is critical to the ability to 

perform and validate mathematical modeling for 

exposure estimation. 


C(t) 

Well Mixed Room Model - Constant 

Contaminant Emission Rate 

G + C ⋅ Q ⎡ ⎛ Q + k ⋅ V ⎞⎤ 

⎛ Q + k ⋅ V ⎞ 

IN ⎢ ⎜ 

L ⎟⎥ 

+ ⎜ 

L 

= 1− 

exp − t C exp − t ⎟ 

Q + k ⋅ V ⎢ ⎜ 

⎟⎥ 

⎜ 

⎟ 

⎣ ⎝ 

V 

0 

⎠⎦ 

⎝ 

V 

L 

⎠ 

Input Variables 

C IN 

V m 3 

K L 

C 0 

mg/m 3 

G mg/min 

Q m 3/min 

per min 

mg/m 3 


Concentration in incoming air 

Generation Rate 

Exhaust air flow 

Volume of Room 

Loss Pathway (sinks) 

Initial concentration

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

0 

3 

6 

9 

Predicted Concentration at 0.01, 0.1, 1, 3, 4, 5 and 10 

Air Changes Per Hour 

12 

Effect of Ventilation Rate on 

Concentration of Contaminant 

15 

18 

21 

24 

27 

30 

33 

36 


39 

42 

45 

0.01 

ACH 

0.1 

ACH 

1 ACH 

3 ACH 

4 ACH 

5 ACH 

10 

ACH

Thank you! 

Questions? 

Speaker Contact Information: 

Catherine E. Simmons, CIH 

Boelter & Yates, Inc. 

Park Ridge, IL 

csimmons@boelter-yates.com

Using Carbon Dioxide as a Tracer Gas to Measure Air Change Rate ...

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