CHEMICAL PROPERTIES—FLAMMABILITY, HEALTH AND REACTIVITY 0.0% 0.4% 000% 10% 1% 20% 4% 100% UEL LEL 15% 25%
FLAMMABLE RANGE
0% LEL 10% LEL
EXPLOSIVE LIMIT
FIGURE 2.8 Flammable concentrations of methane. The flammable range of natural gas in emergencies is not just two numbers
on a MSDS. It is a tangible, invisible zone at the natural gas emergency scene. “Street Smart” responders know that where they stand is crucial to their sur- vival. If you are standing within the flammable range and ignition does occur, you could be seriously injured or killed. Emergency responders must always be careful to avoid entering this area. Obviously, to do so is fool-hardy. So where do we draw the line? The lower explosive limit (LEL) cannot be the delineation because even here you could still be injured or killed. A more practical safety guideline has been developed by OSHA to increase safety in emergency response to flammable atmospheres. In atmospheres at 10% of the LEL (.4% natural gas in air) evacuate the area. In atmospheres greater than 10% no action should be taken. Responders could be entering explosive at- mospheres. With any reading, they should be cautious, use a defensive oper- ation and/or wait for assistance from the utility company. Since human senses can only detect the odor which occurs at much smaller
concentrations, responders may need some form of instrumentation. The most common tools are a Flammable/Combustible Gas Indicator or a Flame Ionization Detector (FID). These devices are sophisticated detection tools used by the local distribution companies.
Ignition Temperature (Point)
Ignition temperature or ignition point is the specific temperature of a heat source that will cause ignition of the material. The ignition point or temper- ature of natural gas ranges from 990ºF to 1100ºF depending on its blend or mixture. This heat can be supplied by open flame, spark, internal combustion engines, catalytic converters on patrol cars, or other ignition sources. If the temperature of the source is higher than any product’s ignition temperature
31
STREET SMART TIP
Remember, odorized gas can be detected at very low levels. 4 ppm is equivalent to .004%, well below .4% (4000 ppm) of gas in air, which is equivalent to 10% of the lower explosive level.
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