This paper covers the investigation and recognition of various types of explosions and ruptures on the basis of information derived from inspection of the debris rather than information gained through interrogation and taking of statements. Several basic concepts which must be understood in order to make the proper explosion investigation are explained. Checking and plotting the pattern of outward pushing or heaving of the walls and partitions of the structure will help in locating the areas in which the heaviest explosions occurred. If gas is the suspected fuel, a careful inspection of all piping is needed to see if the piping may have been cracked and leaking before the explosion. The inspection of underground lines for leakage is especially important since gas may leak from a line and pass through the soil before accumulating in an area such as a crawl space. The explosion site should be checked carefully for pieces of debris that were blown away from the site of the explosion when the initial explosion occurred. The interior of a structure should also be checked for the possibility that the gas regulators may have failed and allowed large quantities of gas to come through the appliances and accumulate. The ignition source is a very necessary, but secondary, consideration once an accumulation of flammable mixture has occurred: almost every occupied structure contains a number of different ignition sources. Several other sources of explosions and explosive material which may commonly be encountered in making explosion investigations are sewer gas, simple air compressors and compressed air receivers or tanks, freon compressors, and common dust.