MadSci Network: Other |
Charlotte, You are correct about a strike back occurring when you light a Bunsen burner with the air vent open. The reason this occurs is due to the right mixture of air and natural gas. There are two physical properties of all flammable gases, an upper explosive limit (UEL) and lower explosive limit (LEL). For natural gas the LEL is 3.8-6.5% and UEL is 13-17%. This means that natural gas will only burn when its concentration is between 3.8 and 17%. When you close off the air vent, you do not allow air to enter the Bunsen burner, thus you allow the concentration of the natural gas to exceed the UEL and burning will not occur. When you light it and open the air vent you allow a flow of air in with the natrural gas and it mixes before coming out the top where the burning is now occurring. There is a flame at the jet but it will not enter the jet becasue the concentration of natural gas immediately inside the jet above the UEL. It is dangerous in that you expect the flame to come out of the burner tip and instead you get a pop at the base. If you hands or other obects are close by you may get burned or cause a fire. Hope this answers your question. Carlin Gregory Staff Chemist Texas Gas Transmission
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