CFD Apparatus History – Fog Pressure Units

In response to inquiries regarding the Fog Pressure Units deployed by the Chicago Fire Department during the early 1960s, Bill Post recently shared this insightful historical perspective: "The primary aim of these Fog Pressure Units was to deliver a powerful stream of water directly onto fires swiftly—faster than conventional engine companies could connect to hydrants and lay out hoses. This capability proved especially valuable in scenarios like expressways, narrow alleys, railroad embankments, and areas with limited hydrant access or water supply issues. When the Chicago Fire Department acquired and began deploying these units between 1961 and 1966, only around 11 or 12 engine companies had booster tanks. For almost a decade—from 1955 to 1966—the department hadn’t purchased any new engines. Of the few new additions, only the final batch of ten 1956 B model pumpers came equipped with 200-gallon booster tanks. A couple of older models had been retrofitted with similar tanks, but these were rare exceptions. The Fog Pressure Units featured 300-gallon water tanks and two booster reels of thin-diameter hose. Their specialized fog nozzles emitted fine, mist-like streams of water under high pressure, giving rise to their name. Except for the first unit, which was built on a Willys Jeep chassis with a John Bean pump, the rest utilized International Harvester chassis fitted with Darley pumps and custom bodies. Most of these units were stationed in high-fire-volume areas on the city’s west and south sides, while one—Fog Pressure 2—was placed at O'Hare Field, using the original Willys Jeep apparatus. Additionally, they served as secondary vehicles for all three Snorkel Squad companies, offering greater tactical flexibility and allowing them to transport extra personnel and gear. By 1964-65, the department had acquired three longer-bodied Fog Pressure Units specifically for the Snorkel Squad companies. As newer engines with larger 500-gallon booster tanks entered service starting in 1967, many Fog Pressure Units were reassigned from stations receiving these modern engines. By 1970, all but two Fog Pressure Units had been retired: Fog Pressure 2 stayed at O'Hare Field, and Fog Pressure (SS1A) remained with Snorkel Squad 1. Most were taken out of service between 1968 and 1969, including those assigned to Snorkel Squads 2 and 3, which were disbanded in 1969. During its peak period in 1966-67, there were 12 active Fog Pressure companies (excluding those assigned to Snorkel Squads). However, within just two years, nearly all of them were decommissioned, except for the aforementioned exceptions. As noted earlier, Fog Pressure 31A briefly served at Truck 31's new station for over a year as a temporary measure until Engine 64 moved into the location. At their zenith, we had a dozen Fog Pressure companies operational, not counting the units assigned to the Snorkel Squads. Yet, within two short years, almost all were phased out, leaving behind only these notable exceptions." —Bill Post

Structural Steel Pipe

The structure Steel Pipe has hot - rolled seamless steel tube and welded steel tube.The seamless steel tube for structure is divided into two types according to the provisions of "seamless steel tube for structure" (GB/ t8162-2008) : hot rolling (extrusion, expansion) and cold drawing (rolling).The outer diameter of hot-rolled steel pipe is 32-630mm and the wall thickness is 2.5-75mm. The outer diameter of cold-drawn steel pipe is 5-200mm and the wall thickness is 2.5-12mm. Welded steel pipe is made of Steel Plate or steel strip after crimping and forming, which can be divided into straight welded steel pipe and spiral welded steel pipe.The outer diameter and wall thickness of the direct-welded steel pipe are 5-508mm and 0.5-12.7mm respectively, which shall comply with the provisions of GB/ t3793-2008.The welded steel pipe for low-pressure fluid transportation is also called common welded pipe, commonly known as clark pipe. The specification is expressed in mm of nominal diameter, which should comply with the provisions of GB/ t3091-2008 for low-pressure fluid transportation.

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