The IFC and IBC are written based on the Maximum Allowable Quantity (MAQ) of the hazardous materials involved. Many will look at the tables and find their MAQ; however, the footnotes contain a lot of liberties that could quadruple the MAQs if certain designs are in place.
Given this basic understanding of maximum allowable quantities and control areas, the various options in the code for increasing the quantities of hazardous materials within a building are as follows:
- Buildings are generally allowed to have up to the basic maximum allowable quantities of hazardous materials without restriction with respect to separations or protection. In this case, the entire building is designated as a control area. The boundaries of the control area are the boundaries of the building (i.e., exterior walls, roof, and foundation).
- Using the footnotes to Tables 307.1(1) and 307.1(2), the maximum allowable quantities can often be increased by providing automatic sprinkler protection throughout the building and/or by using approved storage cabinets, safety cans, or other code-approved enclosures to protect the hazardous materials. It is important that the increases identified in the footnotes only be used where applicable.
- Four other options are available to further increase the quantities of hazardous materials in any building:
- Provide additional control areas as limited by Table 414.2.2,
- Provide one or more firewalls in conformance with Section 706,
- Apply the allowances for unlimited quantities in Section 307.1.1, or
- Construct the building as required for a Group H occupancy.
Assuming additional control areas are used, each additional control area MUST be separated from all other control areas by minimum 1-hour fire barriers or 2-hour fire barriers if required by Section 414.2.4.
Vertical isolation of control areas MUST be accomplished by floors having a minimum 2-hour fire-resistance rating.
The permitted number of CONTROL AREAS decreases vertically through the building, as does the quantities of hazardous materials per control area. As with many other conditions regulated by the code, a key factor is the ability of the fire department to access the incident area. The higher the hazardous materials are located in the building, the more restrictive the provisions become, owing to the limitations on fire department access and operations.
The number of control areas permitted within a SINGLE STRUCTURE may also be increased by dividing the structure into two or more buildings with FIRE WALLS. The limits on control areas can be applied independently to each portion of a structure separated by fire walls complying with Section 706. As a result, an increased amount of hazardous materials may now be present without classification as a Group H occupancy where fire walls divide a structure into separate buildings.
One other fundamental concept involved in applying the maximum allowable quantities is the “situation of material.” The maximum allowable quantities in the code are based on three (3) potential situations:
- storage,
- use-closed, and
- use-open
Though not defined by the code, the term storage is generally considered to include materials that are idle and not immediately available for entering a process. The term “not immediately available” can be thought of as requiring direct human intervention to allow material to enter a process or as using approved supervised valving systems that separate stored material from a process.
In the case of liquids and gases, storage is generally considered limited to materials in CLOSED VESSELS (e.g., not open to the atmosphere). For example, materials kept in closed containers such as drums or cans are in storage because deliberate action (opening the drum or can) would be required to use the material. However, when a container or tank is connected to a process, the question arises whether the material in the container or tank is in storage or in use.
In general, the quantity of material that would be considered to be in use is the quantity that could normally be expected to be involved in a process, or that could reasonably be expected to be released or involved in an incident as a result of a process-related emergency. Consider a process having hazardous materials that are piped from an underground storage tank outside of a building to a dispensing outlet within a building. Because the tank is connected to a process within the building, it could be argued that the contents of the tank are available for use in the building (see definition of “Use” (Material) in IBC/IFC Section 202) and that the amount should be counted toward the maximum allowable quantities.
However, if an approved, reliable arrangement of valving is provided between the supply and the point where the material is dispensed, it would be reasonable to conclude that the quantity on the supply side of such valving that is outside of the building would be unlikely to impact incidents occurring within the building and, therefore, need NOT be counted toward the maximum allowable quantities. This reliable arrangement of valving can be considered an interruption of the connection between the material in storage and the point where the material is placed into action or made available for service.
The difference between USE-CLOSED and USE-OPEN is basically whether the hazardous material in question is exposed to the atmosphere during a process, with the exception that gases are defined as always being in closed systems when used insofar as they would be immediately dispersed (unless immediately consumed) if exposed to the atmosphere without some means of containment.
Source: IBC/IFC