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Old 12-09-21, 11:28 AM
Mad bike riding scientist
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Originally Posted by Schlafen View Post
Petrol only ignites from open flame.
Only petrol, no need for a flame thrower on this job, lol.
Petrol (or gasoline for this side of the pond) doesn’t need an open flame to ignite. It just needs a spark. It’s very easy to ignite.

Fumes from like 500ml of petrol in an open space igniting? Not even Bear Grylls can make that fire.
No. Pour out 500 ml of gasoline and throw a match at it. It will ignite before the match hits the pool of fuel and will likely ignite much closer to you than you think.

What will set the petrol on fire, will set acetone, mineral spirits or alcohol on fire too. If that's a concern for people (clumsy or whatever) stick to water based degreasers, don't risk it, bike maintenance is not that important, lol.
While what can set gasoline on fire can start those other solvents on fire, it is far easier to ignite gasoline than it is to ignite any of those other materials. Acetone has a flash point of 0°F (-18°C). Ethanol has a flash point of 55°F (12°C). White spirits (also known as mineral spirits) have a flash point that depends on the grade of the mineral spirits but varies from 70°F (20°C) to 130°F (55°C). The higher the flash point, the harder it is to get a fire started. These materials can’t be used around open flame but they won’t easily make a vapor cloud that will find an ignition source, either.

Gasoline has a flash point of -50°F (-45°C). That means it is easy to ignite and requires very little energy to do so.

Originally Posted by easyupbug View Post
While you are correct a caution to readers, the ignition temperature of gasoline is super high, something like 500ºF, what often gets people in trouble is not only an open flame but even a small spark which will ignite gasoline vapors at any temperature.
That’s the auto ignition temperature. Heat an air/fuel mixture of gasoline to that temperature and it will combust spontaneously. That’s not the problem. Gasoline has a “piloted ignition temperature” of -45°F (-43°C). A piloted ignition temperature is

In other words, at any temperature that you may use gasoline at, it can ignite if it finds an energy source…and energy sources are everywhere.
Stuart Black
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