A common misconception is that cooling towers are inherently safe from fire hazards because water flows through them. However, cooling towers can be highly vulnerable to fire risks because they contain many combustible materials such as polypropylene (PP), polyvinyl chloride (PVC), polyethylene (PE), wood and fiberglass-reinforced plastic (FRP). These materials can be found in the form of many standard cooling tower components such as the tower structure, fill, drift eliminators, piping, louvers and fans.
Because such hazards exist, some manufacturers in the process industries, depending in their manufacturing processes, may find it prudent (or required) to seek equipment with FM Approval. As FM Global notes on its website, “FM Approvals’ certification process ensures customers a product has been objectively tested and conforms to the highest international and most national standards.” Products and services that are FM Approved are specification tested to protect their properties from loss.
Cooling towers can meet FM Approval standards in two categories:
- Utilization with a sprinkler system.
- Utilization without a sprinkler system.
This article will focus on meeting the standards without automatic sprinkler protection. The purpose of seeking this type of FM Approval for a cooling tower (Class FM4930) is to allow an owner to eliminate the associated costs — initial purchase as well as ongoing maintenance over the lifetime of the system — that come with the utilization of a sprinkler system.
Every facility and process is unique, and not every application requires an FM Approved cooling tower. The determination is a risk-assessment and loss-prevention measure based on each owner’s unique requirements and insurance coverage.
Testing A Cooling Tower for FM Approval
The key step in the FM Approval process for industrial cooling towers involves building a full-sized representative tower cell that contains the specific configuration of components to be included as part of the system design. This can include structural members, wall panels, decking material, fans, louvers, fill, drift eliminators and water-distribution systems.
The system is evaluated as a whole based on its ability to “withstand damage from fire exposure and retain operational integrity and not impose a fire hazard to adjacent structures or surroundings.” The test procedure involves igniting a specified amount of heptane fuel and then witnessing the burning characteristics of the tower with its specific configuration of components.
Approval is based on the amount of damage, loss of operational capability, structural integrity of the tower cell and fan support, and containment of the fire. The cooling tower cell should contain the fire within the cell so as not to allow the propagation of the fire to adjacent cells or structures. For single-cell cooling towers, their design should contain the fire in such a manner as to have at least 75 percent of the operating capacity available after the fire event.
Can Individual Components be FM Approved?
It must be noted that FM Approval does not approve individual components for use in cooling towers. Approval is only extended to the entire cooling tower system as it was tested and the components contained within it as a complete system.
While the FM Approval standard lists various components that are included as part of an FM Approved tower design, those components are only listed as a reference for FM Approved cooling tower systems. As FM Global notes, these components are FM Approved only “for use when installed in the prefabricated factory assembled units as described.”
As an example, suppose ABC Cooling Tower Co. builds tower model CT100 that contains Fill 123. Model CT100 is tested by FM and receives FM Approval. It does not follow that Fill 123 can be installed into model CT999 to make CT999 an FM Approved tower. It also does not mean that model CT999 utilizes “FM Approved Fill.”
The ramifications of this go even further. For instance, suppose an FM Approved galvanized-steel cooling tower is being repaired or rebuilt, and OEM components that are identical to the original parts are used in the refurbishment. But, the cold water basin is sand-blasted, sealed and coated to prevent corrosion. In such a case, the basin coating may invalidate the FM Approved status of that tower. This is because the coating used on the basin was not part of the original tower that was FM burn-tested and approved. Often, such coatings are flammable materials.
Approvals for New vs. Retrofit Towers
Tower manufacturers run full-scale tests on new cooling towers to determine if the tower design is capable of preventing the fire from propagating to adjoining cells (for multi-cell designs). These tests provide owners with confidence that the tower design is able to limit the effects of a fire event.
A common misconception is that fouling will increase fire potential or negate the effectiveness of an FM tower design. In most cases, the accumulated materials are solids, minerals, muds and salts, and biologicals that are found within the circulating water. These are materials that may cause, or be the result of, scaling or fouling in a cooling tower. These materials are not typically viewed as a source of increased fire potential in FM Approved cooling tower applications.
One instance where the materials might increase a tower’s fire potential would be in the case of a pulp or paper mill where there may be an accumulation of combustible fibers. If these organic fibers were to dry out and ignite from an outside source, then there would be potential for additional heat from the combustion as compared to an FM burn-tested tower.
Typically, the fill, piping, drift eliminators and structure itself are the most flammable components of the cooling tower. Unless the buildup of material is of a flammable nature, there should not be an increase of fuel to burn compared to when the tower was tested as new.