Oxygen-Limiting--One type of vertical silo is an “oxygen-limiting” or “controlled atmosphere” silo. The purpose and function of this type of silo is just as the name indicates: to limit oxygen as the silage is stored. While the conventional silo is constructed to minimize the free flow of air into the storage area, the oxygen-limiting silo is designed as solid construction to be nearly air-tight. They are commonly constructed of steel shells with an inner layer of glass bonded to the steel to protect it and augment the insulation properties. The outer covering may be a finish of a ceramic and enamel coating. Poured concrete and fiberglass silos also are in operation today. Conventional silos of poured concrete construction can be converted to function as oxygen-limiting silos. The danger here is that these silos appear to be conventional, but they are actually oxygen-limiting and must be treated as such. The primary characteristics will be no silo openings, no unloading chute, and a fill pipe extending into the top of the dome. Conversion will also be identified by the bottom-unloading configuration. Main features--The primary identifying feature of oxygen-limiting silos is the absence of an unloading chute on the exterior of the silo. Common characteristics of oxygen-limiting silos can also include a fill door located in the center of the top of the silo roof, a roof hatch rather than a loading door, a center fill pipe attached to a blower or fill pipe, or a single unloading door at the bottom of the silo. Oxygen-limiting silos primarily use bottom unloading--filling from the top and removing silage from the bottom. Most oxygen-limiting silos also have a steel ladder and safety cage leading up to and across the roof to the center fill door. (See Diagrams 3 and 4.)
Other features that may be found on oxygen-limiting silos include two-way pressure relief valves on the roof, roof hatches, and access doors at ground level with safety interlocks. Two-way pressure relief valves compensate for interior pressure changes caused by temperature variations. (Diagram 5.)
Oxygen-limiting silo may also be equipped with a “breather bag” arrangement designed to compensate for pressure changes in the interior of the silo. (See Diagram 6.) Warnings or safety decals may be posted on oxygen-limiting silos. These are primarily intended for farm workers in a routine setting. Firefighters should consider fires or incidents in an oxygen limiting silo as an imminently hazardous situation, which could result in death or serious injury.