Benzene is a constituent of gasoline. It is a cancer-causing chemical, and is a liquid at normal temperatures. It is a heavy gas when it evaporates. Its molecular weight is 78.11 kg/kmol. The IDLH of benzene is 500ppm. It boils at 176.16 degrees Fahrenheit, and freezes at 41.95 F. There are no models for a spill of benzene in a cold temperature setting (Portland, Maine) because at 40 F and at 20 F, the benzene does not evaporate and ALOHA will not show a footprint. The vapor pressure of benzene is 0.17 atm. Benzene has a CERCLA RQ of 10 pounds. So if 10 pounds of benzene are released at a facility, this must be reported to all response authorities, meaning the facility must notify the National Response Center, the LEPC, the SERC, and the local fire department. There is no standard set for benzene under EPCRA, so the 10,000-pound threshold applies for Tier Two reporting.

The "footprint" of a heavy gas like benzene is very different from a "footprint" of a light gas like ammonia. The heavy gas spreads out more the further it travels from a spill, covering more area in proportion to the distance its plume reaches than a light gas. A good breeze has a narrowing effect on the shape of the plume. The plume from a 500 pound spill (about one barrel) of benzene would travel about 1/10 mile before dissipating below the IDLH.

Benzene Phoenix, AZ Urban/Rural Day 90°F and Night 68°F at 5k and 20k

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500 lbs

5,000 lbs

50,000 lbs

500,000 lbs

5k/Urban/day 90°F

248 yds/0.14 mi

735 yds/0.42 mi

1,684 yds/0.96 mi

2.4 mi

5k/Rural/day 90°F

324 yds/0.18 mi

879 yds/0.50 mi

1.2 mi

2.8 mi

20k/Urban/day 90°F

178 yds/0.10 mi

582 yds/0.33 mi

1.1 mi

3.0 mi

20k/Rural/day 90°F

219 yds/0.12 mi

718 yds/0.41 mi

1.3 mi

3.2 mi

5k/Urban/night 68°F

249 yds/o.14 mi

710 yds/0.40 mi

1,631 yds/0.93 mi

2.4 mi

5k/Rural/night 68°F

322 yds/0.18 mi

784 yds/0.45 mi

1.1 mi

3.0 mi

20k/Urban/night 68°F

173 yds/0.10 mi

571 yds/0.32 mi

1.1 mi

3.0 mi

20k/Rural/night 68°F

214 yds/0.12 mi

707 yds/0.40 mi

1.3 mi

3.2 mi