May 2004

A Closer Look at Suppression-Mode Upright Sprinklers

Our August 2003 article briefly described the different types of suppression-mode sprinklers. We’ll now explain the reasons leading to the development of suppression -mode upright heads.

When suppression-mode sprinklers were first being developed, a problem came up with upright-type heads. The sprinkler piping became a significant obstruction to the distribution of water needed to effectively suppress a fire. In most cases, this lead to an excessive number of heads opening (the design criteria for suppression-mode sprinklers is to have no more than 12 heads operate). Technology at that time could not determine how to overcome that problem so pendent-type heads (the heads were located below the piping) were advanced.

The negative effect of using pendent heads was that they did not lend themselves to retrofitting on most existing systems. While advances in pendent heads evolved with even larger sizes, overcoming the problem of the upright heads continued to be researched.

The problem of obstructions was overcome through modifications to the heads and the first head was developed using a nominal k-factor of 11. Eventually larger upright heads (k-factors of 14 and 17) were developed.

Although larger upright heads may be developed, the k-factor 17 head may be the largest size used on retrofit systems. This head uses a 3/4 in. pipe thread (the largest pipe thread currently used for control-mode sprinklers); larger k-factors would start to compromise the mechanical strength of the head of the suppression-mode sprinklers.

The upright heads currently do not have the same range of commodities that can be protected by pendent heads. Notably, this includes uncartoned expanded plastics, roll tissue paper, aerosols and flammable liquids. Further testing may well see protection criteria expand into these commodities.

If you would like further information regarding the use of suppression-mode upright sprinklers, please contact Risk Logic Inc.