What are the limits for blast furnace gas and coke oven gas**, and how is a gas explosion test conducted?

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When combustible gases, combustible dusts, or vapors of combustible liquids mix with air (or oxygen) to reach a certain concentration, **will occur upon contact with a fire source**. The concentration range within which **can occur in response to a fire source** is known as the **limit**. **The limit is usually expressed as the volume percentage (%) of combustible gases, combustible dusts, and combustible liquid vapors in air. When combustible gases, combustible dusts, or vapor of combustible liquids are present in the air at certain concentrations, they will ignite in the presence of a fire source. The lowest such concentration is referred to as the **lower limit**, while the highest concentration is called the **upper limit**. Gas **usually requires three conditions: (1) there must be a combustion aid (air or oxygen) mixed with the gas, at a concentration within the optimal range ； ⑵There must be an open flame, an electric flame, or a high temperature sufficient to reach the ignition point of gas ； ⑶It is in a confined space or volume, where the lower limit for coke oven gas is 5.5%, and the upper limit is 30% ； The **lower limit** for blast furnace gas is 30%, and the **upper limit** is 75%. The equipment required for conducting an explosion test includes gas analysis instruments, air tubes, and a ** chamber. Using the air tube from the gas analysis instruments, 100 ml of air sample from the site to be analyzed is collected and introduced into the ** chamber; power is then applied to observe whether ** appears. If no ** appears and there are no sparks, work can proceed; however, if ** appears along with sparks, work must not be carried out. Gas samples can also be directly collected using a tube; for experiments involving an open flame, the observation method remains the same. Sampling requires opening the cylinder valve to allow gas to escape, ensuring that all gas inside the sampling cylinder is discharged ； When performing sampling and ignition tasks, pay attention to the direction of the cylinder opening; for blast furnace gas, the opening should be tilted upward ； For coke oven gas, the nozzle opening is tilted downward. After sampling, take the **cylinder to a safe place, open the cylinder lid to ignite it; when the flame burns steadily from the mouth of the cylinder to its bottom without any popping sound, it indicates that the gas can be supplied to the heating system.