Click here for a printable version of this article.

September 2004: Cooling Towers

Cooling towers are very common in commercial/industrial occupancies. They may be used to for air conditioning needs or for process cooling for certain types of production equipment. Towers used for process cooling can be an integral part of production and their loss could result in significant business interruption.

A towers function is to cool water. Warm water is distributed in the tower by spray nozzles, splash bars or filming-type fill in a manner which exposes a very large water surface area to atmospheric air, thus cooling it. The air is circulated either by fans, convective current, natural wind currents or the induction effect from sprays. Via a closed loop piping system, the cooled water is pumped back to the process equipment, extracts heat and returns back to the cooling tower.

Fire protection in the form of automatic sprinklers is most often viewed as unnecessary since the tower is normally wet. However, a high percentage of commercial towers are filled with wood or plastic splash bars and when the tower is not in use, this combustible fill material will burn. In fact, depending upon the construction method, there can be parts of a combustible cooling tower that remain dry even during operation.

There are several types of cooling towers currently in use such as Mechanical/Natural Draft, Counterflow or Crossflow, Induced-Draft or Forced-Draft or a Hyperbolic Crossflow and Counterflow (For a description of the various types, see FM Global Data Sheet 1-6, "Cooling Towers.") Regardless of the type of tower, automatic sprinkler protection may be needed based on the construction material.

Materials commonly used for tower construction are selected to resist the generally corrosive conditions. The material can be wood, plastic, concrete or metal. From a fire protection standpoint, wood and plastic construction are the main concern since there would normally be no fire exposure from a metal or concrete tower.

Wood can be used for all static components, not only the splash bars. Wood can be used for framing or for fan support.

Fiberglass-reinforced plastic materials have a broad use. They can be shaped into complex components such as a piping, fan cylinders, fan blades and structural connecting members. Polypropylene, ABS and other plastics are normally used as fill bars.

There are combustible cooling towers available that have been approved by Factory Mutual Research that can be used without sprinkler protection. They fall into two categories, those being Limited Combustibility or Multi-Cell. Limited Combustibility towers are constructed such that the fire does not continue to self-propagate beyond its point of origin. Multi-Cell towers have individual cell units within the tower. A fire in one cell will have no affect the others.

If your operation utilizes cooling towers that are critical to production, the fire protection associated with them should be reviewed. Risk Logic can assist in inspecting the determining the need for the proper protection required.