Test Methods for the Flammability of Cooling Tower Media

Cooling towers are built from several different materials: wood, metal, and plastics just to name a few. Each of these materials of construction has an inherent risk in its ability to ignite, sustain, and spread a fire event. To properly mitigate the associated fire risk, it’s important for a tower owner/operator to understand how the components in their tower will react during a fire event.

Testing can be completed to outline the relative burning behavior between different materials. For the polymers that typically makeup the cooling tower internals (filldrift eliminatorslouvers, etc.) some common fire evaluation methods include: Steiner Tunnel Test (ASTM E84), Limiting Oxygen Index (ASTM D2863), Cone Calorimeter (ASTM E1354), and the Standard for Safety of Flammability of Plastic Materials (UL94). For this discussion, we’ll focus on the Steiner Tunnel Test (E84) and Limiting Oxygen Index (LOI).


The Steiner Tunnel Test is a large-scale product test commonly found in cooling tower component specifications. Originally developed for the evaluation of wall and ceiling coverings, E84 is a standard test method to evaluate the surface burning characteristics of building materials. This is done by applying two gas burners to one end of a ~2 ft (0.61 m) width x 24 ft (7.3 m) length ceiling mounted sample. The horizontal flame propagation and smoke development are monitored and then used in the calculation of a Flame Spread Index (FSI) and Smoke Developed Index (SDI) value for the tested product.


The LOI test is a small-scale benchtop test used to evaluate the ignition and flammability characteristics of a material, often used as a research and quality control tool. This test method measures the minimum oxygen concentration required to support candle like combustion of a polymer. A controlled mixture of oxygen and nitrogen are pumped into a test tube which houses a vertically supported test specimen. Once the desired oxygen concentration is reached, a pilot test flame is applied to the top of the specimen for a specific duration. The final test value is the highest concentration of oxygen that burns less than 2 inches (5 cm) of the specimen and extinguishes within 3 minutes.


Included in the Cooling Technology Institute (CTI) standard for thermoplastic materials used in film fill, splash fill, louvers, and drift eliminators (STD-136) is a flammability property. Due to the lack of better suited tests at the time, E84 was adopted as the preferred method for evaluating the fire risk of a cooling tower polymer. However, pitfalls inherent in the E84 procedure suggested this product test did not fit well in the materials standard. These pitfalls include:

  • There is no specification on size, thickness, or orientation for a test. Two manufacturers could test a similar product at different gauges and orientations, yielding drastically different results.
  • There is a lack of guidance on how to evaluate materials that may drip, melt, or delaminate during testing. An example of this would be a polypropylene fill media, which will melt and drip during testing, thus halting horizontal propagation and resulting in an inaccurately low FSI result.

In 2020, CTI officially switched the flammability property in STD-136 to the LOI test. Outlining the minimum required oxygen index concentrations, this generally repeatable test method fits well in a materials standard. The LOI test is important in outlining the relative risk of ignition between polymers. Standard atmospheric air consists of 20.9% oxygen at sea level and the use of materials with higher oxygen index values may mitigate fire risk in a cooling tower application.

Whether your cooling tower specification calls out ASTM E84, or has updated to LOI, Brentwood has completed testing to ensure our materials are compliant with CTI STD-136. For specific test results, or for more information on material/product flammability, please contact your customer service representative. For more information on the flammability of materials used in cooling tower media, click the button below and watch our recent webinar, “Flammability of Film Fills: A Comparison.”

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