API RP 2216:2003(2010) pdf download

API RP 2216:2003(2010) pdf download.lgnition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air.
4.2 SIDES OF STORAGE TANKS
Hot surfaces may also cause ignitions in high flash point hydrocarbon storage tanks, Fixed (cone) roof tanks storing small amounts of fuel oil, diesel fuel and lubricants arc more likely to explode when involved in sumunding fires than arc tanks containing low flash products. This is because vapors arc not usually present in these tanks (above the liquid level) when fires occur. A considerable amount of time is required 11r the radiant heat of a tire impacting on the side of one of a high flash point hydrocarbon storage tank, to produce enough vapors to till the empty space above the liquid level with a concentration that is too rich to burn (above the upper explosive limit). If the side of the tank is heated sufficiently enough during the time the vapors are forming, and if the vapor concentration reaches the explosive range at the same time that the side of the tank reaches ignition temperawres, an internal explosion is likely to occur.
4.3 IGNITION OF HEAVY OILS BY HOT SURFACES
Hot surface tires have occuned involving heavy oils such as hydraulic oil, motor oil, lubricating oil and gear oil. One example of such an ignition would be the release of a fine spray or oil mist from a broken or leaking hydraulic line, against an overheated surface, such as that caused by a bearing failure. Allowing a spill or stream of heavy oil to contact a hot surface for a period of time (depending on the surface temperature) that is long enough for decomposition (cracking) to occur, will result in ignition. An example of this sould be a motor oil spill on the hot manifold of an automobile engine.
5 SUMMARY
5.1 GENERAL
All of the testing (to date) indicates that surface temperatures must be several hundred degrees (Fahrenheit) aboe the laboratory measured minimum AITs to ignite flammable vapors in the open air. However, it should be recognized that both pre-fianie ignition and cool-flame ignition may occur at temperatures lower than the AlT (see 3.3). In addition, both wind velocity and ignition lag time will impact the All’ (see 3.4).
The size of the heated surface also aflcts the ability to cause ignition. Heated surfaces may be too small (in size) to cause ignition whereas a flame or large. ignitable spark (such as an electrical spark) could be the source of ignition in an identical situation (same hydrocarbon, same temperature. etc.). In fact. a heated surface may be so small that no mci-ease in temperature will cunipensate fur volume tSLIch as the size of a small piece of hot sparking metal thai results from the use of hand tools u steel surfaces).
It appears that a number of other factors also influence the AlT of a hydrocarbon when contacting hot surfaces. These include the rate of liquid spread on the hot surface, the rate of heat transfer between the heated surface and the hydrocarbon. the temperature and molecular changes within the liquid and the ambient temperature. rate of vaporiiation and diffusion of he liquid. These factors aflct the ability to accurately predict conditions under which auto-ignition will occur when hydrocarbons contact heated surfaces.
5.2 CONCLUSION
The identification of a heated surface as the cause ol ignition can often lead to an incorrect analysis of the real source of ignition. In gencral, ignition of hydrocarbons by a hot surface should not be assumed unless the surface temperature is approximately 360°F (182°C) above the accepted minimum ignition temperature of the hydrocarbon involved. Test data and field experience both indicate that the ignition of flaminable hydrocarbon vapors by hot surfaces in the open air requires temperatures considerably above the reported minimum AITs of the hydrocarbons involved.
Typically, there is little risk of ignition of hydrocartx)n vapors or liquids by hot surfaces under rionnal operating conditions Years of industry experience support this conclusion It is therefore important to recognize and understand the characteristics and nature of ignition of hydrocarbons by hot surfaces in open air, including the impact of ambient temperature. hydrocarbon molecular structure: pressure: the size, composition, temperature and configuration of the hot surface and many other factors, so that investigation of an incident does not result in identification of an incorrect or improper source of ignition.