How flammable is butane?

Butane is highly flammable and is usually used as lighter fluid.

because its hydro carbon and all hydrocarbons are inflamable

water. i don't know what else but I'll get back to you

Because they react dangerously with fire. Thus, they are flammable.

Flammability is defined at how easily something will burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification...