layout well to predict where the smoke will go, and to ensure that the doors ensuring the ventilation remain open by wedging or propping them. The main risk of this method is that it may accelerate the fire, or even create a flash-over; for example, if the smoke and the heat accumulate in a dead end. Hydraulic ventilation is the process of directing a stream of water from the inside of a structure out the window using a fog pattern. This will effectively pull smoke out of room. Smoke ejectors may also be used for this purpose. Categorizing fires United States In the US, fires are sometimes categorized as "one alarm", "all hands", "two alarm", "three alarm" (or higher) fires. There is no standard definition for what this means quantifiably; though, it always refers to the level of response by the local authorities. In some cities, the numeric rating refers to the number of fire stations that have been summoned to the fire. In others, it reflects the number of "dispatches" requesting additional personnel and equipment. Alarms levels are generally used to define the tiers of the response as to what resources are to be used. For example, a structure fire response draws the following equipment: four engine/pumper companies, one truck/ladder/aerial/quint company, and one battalion chief unit. This is referred to as an Initial Alarm or Box Alarm. A working fire request (for the same incident) would call for air/light units and chief officers/fireground commanders (if not provided in the original dispatch). This summarizes the response to a First Alarm fire. Second and subsequent alarms call for two engine companies and one truck company. The reason behind the "Alarm" designation is so the Incident Commander does not have to list each apparatus required. He can simply say, "Give me a second alarm here", instead of "Give me a truck company and two engine companies" along with requesting where they should come from. Categorization of fires varies among fire departments. A single alarm for one department may be a second alarm for another. Response always depends on the size of the fire and the department. United Kingdom In the fire services in the United Kingdom, the scale of a fire is measured by the number of "pumps" (ordinary fire engines) that were present. For example, a fire which was attended by 4 engines would be recorded as a "4-pump fire". See