Is propane safer than natural gas?

Answer 1

This is a difficult question to answer since no indication of the application is provided. It is assumed the question refers to typical household use.

Some things to consider when answering this question:

Upper and Lower Flammability Limits (LFL-UFL)
Methane: 5-15%
Propane: 2.1-10%

As you can see propane burns at lower concentrations than methane but has a smaller range of flammability. Methane has a slightly higher LFL, but has a wider range of concentrations that combustion will occur.

Specific Gravity Referenced to Air
Methane: 0.5537
Propane: 1.5219

Gases that are lighter than air will rise, while gases heavier than air sink and concentrate near the ground. If a leak occurred propane would tend to concentrate near the ground which would potentially expose it to more ignition sources (such as the pilot light on a water heater or an electrical source such as a refrigerator) than methane.

Autoignition Temperature
Methane: 580C (1076F)
Propane: 480C (842F)

Autoignition temperature tells you what temperature that the gas will automatically burn if a leak occurs in the presence of air. Propane has the lower autoignition temperature. It is unlikely that these high temperatures would ever be seen under normal conditions for home use except in a house fire.

Heat of Combustion
Methane: -909.73 Btu/SCF
Propane: -2316.65 Btu/SCF

Propane burns with about 2.5 times the energy per standard cubic foot than methane. As a note this is also what makes propane very useful, because the energy density is higher.

Other considerations

Propane is generally stored as a liquid in tanks in or around the home. Often it is the responsibility of the owner to have the tanks inspected, maintained, and kept in proper working order. Owners must also ensure that tanks are the proper distance from any structures inhabited by people (a rule that is commonly broken, often due to owner ignorance).

On the other hand natural gas cannot be stored as a liquid at room temperature because room temperature is higher than its critical point. Therefore natural gas is transported in pipelines owned by private companies and there is generally more oversight required either by regulations, company policies, or the desire to avoid liability lawsuits.

Both gases are generally safe for use as long as the proper procedures for upkeep are followed; however, propane opens the door to more operator error because many people do not have the technical knowledge to properly handle or maintain the systems. On the other hand propane is often economically advantageous due to its lower demand (and therefore lower price) as well as the high energy density associated with it.