When pure hydrogen is ignited, hydrogen molecules and oxygen molecules contact with oxygen at the ignition point, that is, the mouth of the conduit, but only hydrogen molecules without oxygen molecules exist in the conduit, and no chemical reaction occurs in the conduit; When the hydrogen is impure, the hydrogen in the conduit is in complete contact with oxygen molecules. When the explosion limit is reached, the ignited hydrogen and oxygen molecules in the conduit and container will have a violent chemical reaction. Because the chemical reaction at this time takes place in a limited space, and this reaction will release a lot of heat, and the generated gas will expand rapidly and explode.
When the proportion of hydrogen is higher than the upper limit of explosion limit or lower than the lower limit of explosion limit, both hydrogen and oxygen are insufficient, so it is quiet combustion. If the hydrogen-oxygen ratio is appropriate within the explosion limit, the reaction speed will be fast, and heat will accumulate rapidly and in large quantities, leading to explosion.
Therefore, the purity of hydrogen should be checked before ignition to avoid mixing oxygen with impure hydrogen.
Note: it is impure hydrogen mixed with oxygen, so it will explode, not hydrogen in impure oxygen.