Let’s assume in our paint booth example that the 6 sprinklers require a minimum of 250 gpm at the point of connection to our overhead main. This gives a minimum criterion of 0.4 gpm / sq ft over the most demanding 2000 sq ft, which gives a minimum demand of 800 gpm.

If we use high temp and/or ≥11.2k sprinklers, the design area is reduced to 2000 sq ft. In our paint booth example above, the area is calculated as Extra Hazard Group 2. However, if the minimum discharge from the sprinklers in question is less than the minimum density X area required for the hazard, you must add an additional flow at the cross main to make up the difference. In this text, one is permitted to calculate all the sprinklers in the area. The same wording is located at 23.4.4.2.4 in the 2016 edition. In the 2013 edition, 23.4.4.1.1.4 clarifies how to deal with these areas. In 2013, additional criteria were added in Chap 23. So, you calculate your 6 sprinklers at 0.4 gpm / sq ft and size the piping to deliver the required water. The paint booth is typically calculated as Extra Hazard Group 2. For example, you have a small paint booth with 6 sprinklers.

In the past, we would just calculate all sprinklers in the area and call it a day. Many times during the design of a project, you will have a small area that is required to be calculated, but the total area does not meet the minimum area required per NFPA 13. What do you do when your design area is less than the minimum specified?

Fire sprinkler calculations