Maximum allowable quantity calculator for hazardous materials.

A maximum allowable quantity limits a hazard category in a control area, not a chemical, and each category has its own.

Chapter 50 of the International Fire Code lets a building hold hazardous materials up to a maximum allowable quantity in each control area before it becomes a Group H occupancy. The quantity belongs to the hazard category: every chemical in a control area that is a Class IB flammable liquid is added together against one figure. Four rules decide how the quantities add up, and they are the ones most often misread:

• Each hazard category has its own quantity. The tables give a quantity for each hazard category and class, and each is a limit of its own: one control area may hold up to the quantity of every category at the same time, and different categories are never added together. (2021 IFC 5003.1.1 and Tables 5003.1.1(1) to (4))
• Class I flammable liquids also share one. Class IA, IB and IC flammable liquids also count together against the table's combination row, and within it no class may exceed its own quantity. (2021 IFC Table 5003.1.1(1), note h)
• Storage and use share the storage quantity. Storage, use in a closed system and use in an open system of one category are each limited on their own, and added together they may not exceed the quantity listed for storage. (2021 IFC Tables 5003.1.1(1) to (4), note b)
• A chemical with several hazards counts in each. A chemical that is more than one category, a flammable liquid that is also toxic for one, counts in full against every category it is. (2021 IFC 5001.1)

So a control area may hold its full quantity of Class II combustible liquid, of a Class 3 oxidizer and of a corrosive at the same time, each against its own row. What it may not do is hold 30 gallons of Class IA and 120 gallons of Class IB liquid without sprinklers or cabinets: the two share the 120-gallon combination row.

Two increases apply where the table's notes put them. A building sprinklered throughout doubles most figures, and keeping the material in approved cabinets, gas cabinets or exhausted enclosures doubles them again, but only in the cells that carry the cabinet note. The two are applied one after the other. Then the story: above the first story, and below grade, a control area holds only a percentage of the table, and each story may have only a few control areas, separated by fire barriers of the rating Table 5003.8.3.2 gives.

What this calculator does not read, so a clean answer is not taken for more than it is: the conditions some notes impose (a highly toxic gas only in an exhausted enclosure, the Class 3 oxidizer maintenance allowance), the retail and wholesale allowances of Section 5003.11, fuel in vehicle tanks, and whether a cabinet is an approved one.