Q

Pre-action dry pipe fire sprinklers versus wet pipe sprinklers

A reader wrote in wanting to know if pre-action dry pipe was still the standard in the data center. Expert Lance Harry responds.

Our fire professionals recommend wet pipe sprinklers over pre-action dry pipe primarily for reliability considerations.

In the dry pipe case the advantage is elimination of accidental discharge due to accidental damage to a head. However, that rarely occurs, in fact. On the other hand, the incidents of pre-action systems not working due to maintenance and other system complexity issues is their downfall. Is there a movement towards wet pipe installations in data centers, or is pre-action dry pipe still the standard?

This is an interesting question which can be evaluated in a number of ways. In my opinion, the predominant fire protection systems in a high value asset environment are dry pipe, pre-action sprinklers, OR clean agent / gaseous systems. The use of wet pipe systems in a data center facility does occur, but I would say in most cases, was installed many years ago when the technology for use of either clean agents or pre-action sprinklers was not nearly as reliable as it is today. Specifically, the use of smoke detection plays a key role in both types of systems.

Smoke detection technology today is both exponentially more reliable and more economical than it was just 10-15 years ago. When smoke detection works properly and smoke is detected, a dry pipe pre-action system essentially becomes a wet pipe system.

The decision to use any given system mentioned generally comes down to an evaluation of risk versus cost.

Generically speaking, its reasonable to say that:

  • Wet sprinklers involve the highest level of facility risk due to response from heat only (not smoke) and because of the risk associated with water in the piping 100% of the time. Wet pipe sprinklers will generally be the most economical system of the three.
  • Dry pipe, pre-action sprinklers involve a moderate level of risk because it is still a water based system, and still does not initiate discharge until heat at each head is well beyond what would cause damage to equipment. Maintenance required is a bit more and the systems are generally more complex. Risk is mitigated to some extent because of the multiple actions required BEFORE water is actually discharged, thus minimizing potential accidental discharges or maintenance mishaps. Pre-action systems are more costly than wet pipe systems but slightly more economical than clean agent systems.
  • Clean agent systems involve the lowest level of risk to the facility due to their quick response activation upon SMOKE detection (not heat detection) which can be magnitudes more sensitive than heat detection. The agent itself also causes no damage or clean up in the facility. The cost of clean agent systems will be slightly more than pre-action systems.
This was first published in March 2006

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