CHAPTER 2 UNDERSTANDING UTILITY NATURAL GAS


and the source is located within the flammable limits, an explosion can occur. One of the most difficult tasks for a responder to accomplish at an emergency scene is to eliminate all sources of ignition. Only specially designed facilities can completely eliminate ignition sources with intrinsically safe designed lights, motors and switches. A more practical street approach is not to focus solely on ignition sources. Rather responders should monitor for the flam- mable range and remain well back from the danger zone or 10% of the LEL. If neither of these actions can be done effectively, responders should evacuate and wait for the local distribution company to arrive.


Health Hazards


Natural gas is a nontoxic fuel. However, under the right conditions, it can be a health hazard. It can be an asphyxiation hazard and the odorant can be un- healthy if breathed in for a long time. Improper installation of the gas-fed units can also create dangerous situations.


Toxic By-products of Combustion


Complete combustion of natural gas produces water vapor and carbon diox- ide. However, incomplete combustion, indicated by a yellow rather than blue flame can create harmful by-products such as carbon monoxide (CO), a lethal,


CARBONMONOXIDE CO


740,000 ppm 1,000,000


10-15 Mins.


dizziness & Headache 5-10 Mins.


Cherry red skin violent headache


Headache 1-2 hr.


Headache 2-3 hr.


tlV-tWa Pel


(OsHa) 25 ppm 400 ppm 200 ppm FIGURE 2.9 Concentration levels and physiological effects of carbon monoxide. 32 1,000 ppm 1,200 ppm tlV-C


reddish skin


stel IDLH 3,200 ppm 2,000 ppm 1,300 ppm 400 ppm


10% of LEL


irreversible damage 1 Hour


death or 6,400 ppm


10,000 ppm 1%


Unconsciousness & death 1-3 Mins.


1.2%


12.8% LEL


74% LEL


irreversible damage


death or


12,800 ppm


128000 lel


ppm 100%

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