1. MODULE 5
Complete and Incomplete Combustion Characteristics

2. Introduction
Combustion is a chemical reaction that changes a fuel source into a useful form of energy, such as heat. This module introduces the ingredients and amounts of those ingredients needed for combustion. You will also learn about the outcomes of complete and incomplete combustion.
After completing this module, you will be able to:
Describe combustion characteristics of propane
Name products of incomplete combustion
Describe characteristics of carbon monoxide (CO) and aldehydes
Identify strategies for checking for carbon monoxide

3. LESSON 1
Combustion Characteristics of Propane

4. Requirements for Combustion
The three ingredients needed to start and sustain combustion include:
Fuel: The fuel propane is a hydrocarbon. Hydrocarbons are chemical compounds made of hydrogen and carbon atoms.
Oxygen: The oxygen needed to burn propane is obtained from the air. Air is made up of 20% oxygen, 79% nitrogen, and about 1% of other miscellaneous gases.
Ignition source: The ignition source must provide enough heat to the propane-oxygen mixture to raise the temperature of propane to its ignition temperature.
REMEMBER all three ingredients must be present in the proper proportions for combustion to occur.

5. Limits of Flammability
Flammability limits are the most common way of expressing the proper gas-air mixture needed for combustion. Flammability Limit equals the percentage of propane needed in a gas-air mixture to support combustion. Normally, this value is given in both upper and lower limits of flammability.
Limits of Flammability in Gas-Air Mixture for Commercial Propane (NFPA 58)
Upper Limit = 9.6%. The upper limit is the highest percentage of propane in the richest gas-air mixture that will support combustion.
Lower Limit = 2.15%. The lower limit is the lowest percentage of propane in the leanest gas-air mixture that will support combustion.
Even with all three sources present, combustion cannot occur unless the propane and air are mixed together in the proper proportions.

6. Combustion Ratios
Propane will burn in any gas-air mixture within its upper and lower flammability limits. The ideal combustion ratio is the most efficient ratio of the mixture of gas and the air. The ideal combustion ratio for propane is: 1 part of propane (4%) to 24 parts of air (96%) When the amount of propane in a gas-air mixture approaches the upper or lower flammability limit, propane will burn but not in the ideal manner. This is called incomplete combustion and is an inefficient use of the fuel.
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7. Combustion Ratios cont.
Incomplete combustion:
May yield insufficient heat
May produce harmful combustion by-products such as carbon monoxide.
Most gas appliance burners are designed to burn a gas-air mixture that is as close to ideal (4% propane) as possible. In addition, appliances may be adjusted periodically by a qualified technician to be sure they are as safe and efficient as possible.

8. Ignition Temperature
Even with an ideal mixture of propane and air, there must still be an ignition source for combustion to take place. Ignition sources are usually expressed as the minimum temperature needed for a mixture of propane and air to ignite. The minimum ignition temperature of propane is 920°F. Although that temperature may seem very high, remember that the flame of a match can develop temperatures up to about 3,000°F. Does this seem extremely high? Well, consider this. The flame of a match burns at about 3,000°F. So propane can ignite at a much lower temperature than that. 8 8

9. Common Ignition Sources
Common ignition sources include:
Pilot burner flame
Match flame
Cigarette lighter flame
However, an open flame is not the only ignition source for propane. Other ignition sources include:
Sparks from electric motors
Light switches and thermostats
Lit cigarettes
Static electricity
A vehicle exhaust system
Always use caution around propane installations.
Never permit any uncontrolled ignition sources near propane, and never smoke around propane installations.

10. Heat Value
Burning propane efficiently creates the most heat per unit of propane. The heat produced by burning propane is expressed in British thermal units (Btu). The heat value for propane vapor is approximately 2,488 Btu per cubic foot. Propane vapor is measured per cubic foot. A ratio of 24 parts air to 1 part propane means the mixture consists of 24 cubic feet of air to 1 cubic foot of propane. The heat value for propane liquid is approximately 91,502 Btu per gallon. Propane is transported and delivered to containers as a liquid that is measured in gallons. It is usually used in its vapor state by customers. 10
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11. Heat Value cont.
You must understand the heat value of propane so you can make the right decisions at installation and service jobs.
Heat value is a factor when:
Sizing and selecting regulators, distribution lines, and appliance openings. As an example, you’ll determine the appropriate pipe size based on the total BTU load and the distance of the appliance to the tank.
Converting appliances from natural gas to propane
Determining the correct size tank or cylinder for customer installations Estimating the container filling frequency for delivery routing schedules 11 11

12. LESSON 2
Products of Complete and Incomplete Combustion 12

13. Products of Complete Combustion
To create complete combustion, enough air must be supplied to the combustion process. Complete combustion occurs when propane and air are burned in the most efficient ratio of: 1 cubic foot of propane (4% propane) to 24 cubic feet of air (96% air) Because propane is a hydrocarbon that burns with oxygen, combustion products are always created, even when propane burns at its ideal gas-air ratio. These products are commonly known as flue gases and include water vapor and carbon dioxide 13 13

14. Products of Incomplete Combustion
Incomplete combustion is not only inefficient but also dangerous.
Without enough air during combustion, other products can result, such as:
Aldehydes: A toxic gas detectable by smell
Excessive water vapor: Can be harmful to appliances’ venting systems
Soot: Potentially damaging to property
Carbon monoxide: A highly toxic gas undetectable by smell
Carbon monoxide is the most hazardous product of incomplete combustion and can immediately harm people and animals. 14 14

15. LESSON 3
Carbon Monoxide at Customer Locations 15

16. Lesson Introduction
In addition to leak and odor complaint calls from customers, you may also handle situations involving the presence of carbon monoxide in a customer's home or their business. This next lesson focuses on the most potentially dangerous product of incomplete combustion: carbon monoxide. Because carbon monoxide is an odorless and colorless gas, sometimes it is difficult to detect. In this lesson, you will learn some general guidelines for detecting carbon monoxide. You’ll also learn that exposure to carbon monoxide can make you sick or can even lead to death. The very young, the elderly, people with heart disease, and those under the influence of alcohol, drugs, or medication are particularly sensitive to the effects of carbon monoxide. 16
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17. Lesson Introduction cont.
it is very important that you understand your roles and company policies related to investigating carbon monoxide calls. Many gas suppliers immediately refer customer complaints about a carbon monoxide hazard to the local fire department. However, companies may choose to investigate such customer complaints. In this case, employees should always treat the call as high priority. Always refer to your company policy for specific guidelines and procedures on responding to and investigates carbon monoxide calls. 17 17

18. Investigating Carbon Monoxide
When investigating a carbon monoxide situation REMEMBER:
It has no odor, color, or taste, so it’s hard to detect.
Exposure to carbon monoxide can make you sick or can even lead to death.
It is flammable and can produce an explosion in a wider range of air mixtures than propane.
Instruments used to detect carbon monoxide should provide readings in parts per million.
Note that many gas appliances will generate very small quantities of carbon monoxide. These trace levels are permitted under the American Standard Approval Requirements, and are not considered incomplete combustion. 18
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19. Investigating Carbon Monoxide cont.
The exclamation points on the graphic show how concentration levels of carbon monoxide affect a person based on how long that person is exposed. 19 19

20. Signs of Carbon Monoxide
Check for carbon monoxide in the air if any of the following conditions exist:
A customer complains of chronic headaches or nausea.
Houseplants are dying.
There is a chronic odor and the source or cause cannot be located. Remember, however, this smell could also be an aldehyde.
Excessive water vapor forms on cool surfaces in the house. 20 20

21. How to Check for Carbon Monoxide
Portable carbon monoxide (CO) detectors are used for measuring the carbon monoxide level in the air. This device may be available at local fire departments or from emergency responders, propane marketers, or service technicians.
Key points to remember about portable CO detectors are:
Persons who use them should always be trained in the correct operation of portable CO detectors and follow manufacturer instructions.
Portable CO detectors should be at or close to room temperature before testing the air.
Samples should not be taken if the air temperature is above 125°F. Therefore, it may not always be possible to check flue gases directly. Manufacturers offer special equipment for taking flue gas readings.
Always follow the manufacturer’s instructions. 21 21

22. Where to Check for Carbon Monoxide
There are specific locations in a house or building where tests for carbon monoxide should occur, including:
In the air at head height
Near gas appliances
Close to heat ducts
Near appliance diverters and fire doors on appliances in basements or utility rooms
Always test different areas in the house or building to determine the highest carbon monoxide level. 22 22

23. When to Check for Carbon Monoxide
After arriving at a customer’s house, follow these steps to test for the presence of carbon monoxide.
In the case where an appliance is turned off before your arrival, tests should be made in the following order:
Take the first set of readings in the air before the appliance is started again.
Take the second set of readings just after the appliance has been turned on a minute or two.
Take the third set of readings after the appliance has operated for about 15 minutes.
Remember to always follow manufacturer instructions. 23
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24. When to Check for Carbon Monoxide cont.24 24

25. Aldehydes and Carbon Monoxide
As you have already learned, both aldehydes and carbon monoxide are products of incomplete combustion. However, unlike carbon monoxide which is odorless, aldehydes have a sharp, penetrating odor even at very low levels. If the odor of aldehydes is present, it is very likely that carbon monoxide will also be present. However, if the odor of aldehydes is not present, carbon monoxide may still present a hazard. 25 25

26. Summary Some important points to remember from this module are:
The three ingredients needed for combustion are fuel, oxygen, and an ignition source.
Flammability limits are the most common way of expressing the proper gas-air mixture needed for combustion.
The ideal combustion ratio for propane is 1 part propane to 24 parts air.
The minimum ignition temperature of propane is 920°F.
Products of complete combustion are water vapor and carbon dioxide.
Products of incomplete combustion are carbon monoxide, aldehydes, excessive water vapor, and soot.
Carbon monoxide is very hazardous but hard to detect since it has no odor, color, or taste. 26 26