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API RP 2216:2010 pdf download

API RP 2216:2010 pdf download.lgnition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air.
Hot-flame Ignition: A rapid, self-sustaining, sometimes audible, gas phase reaction of a sample or its decomposition products with an oxidant usually accompanied by a readily visible yellow or blue flame. AlT is defined as the hot-flame reaction threshold temperature.
Cool-flame Ignition: A relatively slow, self-sustaining, barely luminous, gas phase reaction of the sample or its decomposition products with an oxidant. Cool flames are ‘isible only in darkened areas. The Cool-flame Reaction Threshold (CFT) is the lowest temperature at which cool flame ignitions are observed.
Pre-flame Ignition: A slow non-luminous, gas phase reaction of the sample or its decomposition products with an oxidant that it is contacting. The Pre-flame Reaction Threshold (PRT) is the lowest temperature at which an exothermic gas reaction is observed.
The ignition temperatures that are typically reported in flammable and combustible liquid hydrocarbon physical characteristic tables (such as in NFPA 325) are similar to AlT values. However, because the CFT temperature and the PRT temperature arc slightly lower than the AlT, both must be considered when assessing the ignition risk of a specific hydrocarlx)n and a particular system or potential exposure.
The occurrence of hydrocarbon vapor releases in open air constitutes conditions that are very different from those experienced in the standard ASTM laboratory ignition temperature tests described above. Because actual field conditions differ greatly from laboratory conditions, ignition of vapors in open air often requires surtce temperatures considerably different from published ignition temperatures of specific hydrocarbons.
3.4.1 Open Air tests
Small scale laboratory tests that were made on relatively unconfined butane/air (AlT 550°F [287°C]) and gasoline/air (AlT 536°F [280°C]) mixtures determined that metal surfaces had to reach temperatures of approximately 1400°F (760°C) before ignition occurred. A number of other, more realistic tests were made in open air where normal wind and convection currents were present. The results of these tests (see Table 2) were essentially the same for both hydrocarbon droplets sprayed on hot sur1ices and for hydrocarbon vapor- air mixtures released at the hot surfaces8 and verified the results of the laboratory tests.
Another test method developed at the National Institute ol Standards and Technology has been used to conduct short duration AlT measurements of hydrocarbon fuels under atmospheric pressure conditions. AITs were determined under steady flow conditions where the contact time between the controlled hydrocarbon/air mixture and the heated metal
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3.4.3 Effect of Wind Velocity
In open air near a hot surface, the time of contact is only seconds or a fraction of a second because convection currents and normal wind disturbances move a flammable vapor-in-air mixture past the hot surface rapidly. Because the contact time under open-air conditions is so short, the surface temperature required for ignition must be substantially higher than reported minimum AITs. The effect of wind velocity on the surface temperature required for ignition of kerosene (AlT of 410°F [210°C1) was determined in wind tunnel tcsts (see Table 4).
The addition of ethanol, methanol and other oxygenates will slightly alter the ignition temperature of motor gasoline. The ignition temperatures of MTBE, alcohol and methanol fill within the range of ignition temperatures for gasoline (see Table 5). Test data indicated that the AlT of motor gasoline containing up to l0% ethanol is similar to that of straight gasoline. Gasoline blended with ethanol, in contact with a hot metal surface at a temperature of 475°F (265°C) above the published AlT of gasoline, would not ignite. However, gasoline blended with 10% methanol/isobutanol had a tendency to ignite at about 360°F (200°C) above the published AlT of gasoline (because it wetted the hot surface more effectively than the gasoline/alcohol mixture).


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