Chapter 3

Natural Gas Fires and Emergencies

"Of all gas fuels used n the united states, natural gas is the most common. More than half of American homes use natural gas for heating and cooking, and it is being installed in 60 percent of all new homes. Natural gas is composed mostly of methane, with varying amounts of ethane, propane, butane, and small amounts of carbon dioxide and nitrogen. The natural gas intended for domestic use contains 70 to 90 percent methane, with ethane making up most of the remainder. When demand is high, usually in the winter, liquid petroleum gas and liquid natural gas may be used to augment the supply. This practice is known as peak shaving.

Natural gas is nontoxic, but is an asphyxiant and can replace oxygen in a tightly sealed room, possibly causing suffocation. Deadly carbon monoxide, a danger found in manufactured gas, is not present in the natural gas used today.

Odorization
Since it is undetectable without metering equipment, it is a requirement that natural gas be odorized so that a leak can be detected by the user. Typically, mercaptan is the odorant added to natural gas. This Odorization enables us to smell gas at levels as low as one-tenth of one percent in air. The addition of odorant is a crucial safety factor because it makes the gas identifiable long before it becomes dangerous. The hazards associated with leaking natural gas are well known, and as a result , any hint of the telltale odor can be quickly reported to the utility company or a fire department. Sleeping occupants of a dwelling, however, cannot detect leaking gas because the human sense of smell is dormant as we sleep. Even when we are awake, our sense of smell can be turned off by extended exposure to a substance. Thus, a gas odor might become undetectable after a period of exposure to it. Occasionally the fire department will be called to investigate an odor of gas in the hall of an apartment house. When personnel locate the apartment with the offending appliance, the occupant, desensitized by lengthy exposure, might not even be aware of the gas leak. Besides the effects of lengthy exposure, there are certain individuals who, as a result of a medical condition have lost their sense of smell. Firefighters, too, in searching for the source of a gas odor can become injured to the scent, and so loose the trail. When searching for the presence of gas or the source of a leak, it is helpful to step outside occasionally to"reset your olfactory sense, and then to return inside to continue the investigation."

Chapter three discusses the hazards properties and hazards of natural gas, the various emergencies and gas related fires we respond to and their safe mitigation. The topics covered in this chapter include:

• Odorization
• Characteristics
• Distribution Systems
• Natural Gas Hazards
  • Air in a Gas Line
  • Water in a Gas Line
  • Increased Gas Activity
  • Combustion Explosion
  • Loss of Odor
  • Regulator Failure
  • Delayed Ignition
• Flammable-Gas Fires
  • Tactics for Flammable-Gas Fires
• Indoor Gas Leaks
• Tactics for Indoor Gas Leaks
• Outdoor Gas Leaks
  • Tactics For Outdoor Gas Leaks
  
  

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