One common question: What is the maximum square footage my facility can be if we are using flammable liquids?
The answer depends and is based on how much fire protection the construction offers. The more fire protection in the construction, the larger the area allowed. Flammable liquids are classified either H-2 or H-3 use group in the building code. In the H-2 use group the liquids are usually classified as type 1A flammable liquids. In the H-3 use group the liquids are either type 1B or 1C. (1C is the least hazardous and type 1A the most hazardous.)
However, small amounts of flammable liquids are exempt and may not require hazardous use groups. These liquids must be in quantities that meet the requirements of a control area so that they are separated from the rest of the building by a 1 hour fire rating.
Once the exempt amounts are exceeded, the building or building area must be either a H-2 or H-3 use group which is limited in area by the type of construction of the building. Usually type H-2 use group is for processes that have open containers of flammable liquids and
H-3 use group usually is for processes that have closed containers, as in a storage building. The table below shows the square footage allowed for each construction type for H-2 and H-3 building use groups.
| Construction Type | Use Group | |
| H-2 | H-3 | |
| Type I-A | 21,000 s. f. /UL stories | UL area / UL stories |
| Type I-B | 16,500 s. f. /3 stories | 60,000 s. f. / 6 stories |
| Type II-A | 11,000 s. f. /2 stories | 26,500 s. f. / 4 stories |
| Type II-B | 7,000 s. f. /1 stories | 14,000 s. f. / 2 stories |
| Type III-A | 9,500 s. f. /2 stories | 17,500 s. f. / 4 stories |
| Type III-B | 7,000 s. f. /1 stories | 13,000 s. f. / 2 stories |
| Type IV | 10,500 s. f. /2stories | 25,500 s. f. / 4 stories |
UL= Unlimited
In addition to the areas allowed in the table above, the more open area there is around the exterior of the building for access to fighting fires, the more additional square footage is allowed; up to an additional 75 % if there is 100% access around the building.
This calculation also gets more complicated in a mixed use building or a building with a number of different building use groups as per the building code. In a building that has a large storage area of non-flammable materials, use group S-1, a office area that may house R&D labs, use group B, and a H-2 or H-3 use group, you would have to calculate each area with the formulas found in the building code to see if the combined square footage of each use group when added together would meet the area limits allowed in the building code.
Taking this into consideration, when should you build a new building vs. finding one?
We cover this concept in more detail in other posts, but with respect to fire ratings: if you can find a building that meets the height and area needs of your company, and can be effectively modified to suit the fire rating needs of your chemical process, then it is likely more economical than finding a suitable site and constructing a new building.
