Repost of an email from Matt Krogh, Extreme Oil Campaign, STAND
[See also High Hazardous Flammable train placards to watch for. – RS]
Empty tank cars and tank car cleaning resources
…here are a couple of government, industry, and expert sources. re the likely volume of crude oil in a given “empty” residue tank car with a hazmat placard:
Heel: the crude oil residue in the bottom and on sides of the tank car
Clabber: consolidated scunge from many uses w/out cleaning
This document for Customs and Border Patrol provides a sample estimate of oil tank cars having 7% heel, or 2,100 gallons for a 30,000 gallon car (p.7):
This document by the American Petroleum Institute explains the different ways they measure heel, and also supports the likelihood of 7% heel. It also contains this statement, which raises concerns about fluctuating vapor pressure and off-gassing: https://www.api.org/oil-and-natural-gas/wells-to-consumer/transporting-oil-natural-gas/rail-transportation/api-rp-3000 “Classifying and Loading of Crude Oil into Rail Tank Cars”
Crude oil expands and contracts based on changes in temperature. For example, the volume can change by 0.4 % to 0.6 % per 10 °F change depending upon the density. Volume corrections shall be carried out in accordance with API MPMS Ch. 11.1-2004 or API MPMS Ch. 11.5, as appropriate.
This formal filing by Phyllis Fox explains how tank cars vent toxic gas, including residue cars, and why temperature changes can cause tank cars to vent:
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