This YouTube video from "NFPA Joe" explains the difference between standard response and quick response fire sprinkler heads. The video explains that the primary difference is the size of the bulb, with quick response sprinklers having a smaller bulb, which allows them to activate faster. The video details how the response time index (RTI) is measured and how it is used to classify sprinkler heads as quick response or standard response. It then discusses the historical development of fire sprinklers and how the need for faster responding heads led to the creation of quick response sprinklers. Finally, the video outlines the different hazard classifications and explains how the choice between quick response and standard response sprinkler heads depends on the combustibility and rate of heat release of the materials present in a given space.