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Testing and Certification of Steelwork Fire Protection

It is important that published test methodology is followed closely, and that products and systems are tested consistently and correctly to maintain the desired fire protection.

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Testing and Certification of Steelwork Fire Protection to UL 1709

Executive summary

With fire safety as critical as ever, it is important that published test methodology is followed closely, and that products and systems are tested consistently and correctly in order to maintain the desired fire protection. Any deviation from the approved individual design details will likely void the fire performance and not provide the necessary protection, which can be critical to life safety.

Robust certification processes detailing the acceptable design, and following correct testing will provide a means of reassurance that the product and system covered by the certification will perform as intended. The designs should be followed closely to provide the necessary fire safety.

This article outlines the requirements for products and systems evaluated against UL 1709, the Standard for Rapid Rise Fire Test of Protection Materials for Structural Steel, also known as the Standard for hydrocarbon-type fires. This article also explains why it is important to follow the requirements within the standard. 

Introduction

During these increasingly critical times for fire safety, it is more important than ever to help ensure the requirements of the Standard are followed by all certification body staff to help ensure consistency of evaluation. The certification through an accredited third-party gives trust and confidence in the result. This, in turn, guides the specifier and/or end-user to make a consistent, technical judgment regarding a product’s suitability for a particular application(s). This is true for all test methods but is even more critical when the application is in a high-risk environment, such as a petrochemical facility or a high-rise building.

As a standard developing body, Underwriters Laboratories has a deep, fundamental interest in developing Standards that are relevant to all parties so that the safety above objective is met. This has been true for UL since its first Standard was issued in 1903 and remains the case today. As the users learn more about the tests and as the products and systems develop, often the methodologies included in published Standards need to evolve. This is currently the case with UL 1709. 

This Standard, for the testing of protection materials for structural steel in rapid rise fires such as petrochemical installations, is co-published with ANSI and was first published in 1991. The early editions of UL 1709 took a rather simplistic approach and was silent on the number of specimens, size and duration. Critically the standard specified the required calibration method for the test furnace to help ensure consistency between laboratories. The Standard, now in its fifth edition, still includes the calibration requirement but has developed to include testing protection to structural beams and a means of evaluating various steel sizes and shapes and for various time periods. The fifth edition provides a much more industry-relevant document than when first published almost 30 years ago.

This development results from working with many levels of interested parties from within the fire safety industry via the standards development process. It is clear that the adoption of UL 1709 as a means of evaluating the fire protection to structural steel continues to be widely adopted, and manufacturers of protective systems are increasingly adopting this as the main hydrocarbon test method to show compliance of their products.

This significant and increased level of adoption has led to more test facilities being available to conduct the tests, leading to different interpretations of the test methodology. This is clearly not ideal given the original stated objective, and the purpose of this text is to provide some much-needed clarity on some areas within the test method.

Furnace calibration

The current method for calibrating the furnace requires a single calibration column to be placed centrally within the furnace chamber. This is intended to reflect what will happen in the subsequent type of testing, thereby exposing the sample under test to the same thermal dose as the calibration column and ensuring a high level of consistency in evaluating the protection system from test to test.

It is not intended that more than one specimen is included in the furnace at the same time as this will result in one or more sides of the columns being shielded from some of the heat within the furnace chamber such that the intended Time-Temperature (t-T) and heat fluxexposure to the specimen is not replicated. This practice is also likely to result in some columns being nearer to the walls of the furnace chamber, which can also result in a lower thermal dose on the protection system under evaluation.

Furnace thermocouples

According to UL 1709, the furnace should be calibrated using eight thermocouples at a maximum distance of 102 millimeters from the exposed face of the specimen. That means eight thermocouples per column to ensure that the furnace temperature is controlled such that the test specimen is exposed to the intended t-T curve. These thermocouples must also be evenly distributed throughout the furnace to ensure an even evaluation of the thermal dose during the test. Uneven distribution of the thermocouples within the furnace chamber is likely to cause a heat gradient, causing uneven heating of the column(s). 

Furnace control

As with most furnace testing, there are variables due to the very nature of the equipment being used. The Standard provides guidance on the level of acceptable variation, in particular with the temperature within the furnace chamber. The intention is that the tolerances are there as guidance to compensate for fluctuation and not to be used in continuous operation. In the ideal test, the tolerances would not be used and would operate within the mean values. To operate the furnace such that it runs toward the lower or upper tolerances will give a lack of consistency between tests as well as between protective systems being evaluated. This is of particular concern when the lower range of tolerance is targeted. This practice should not be followed, and test data generated via a test operated at the lower end of the tolerances throughout the test should be treated cautiously with the understanding it may not perform as other products evaluated to the prescribed fire curve.

Specimen thermocouples

UL 1709 is clear in the number of thermocouples to be used on each specimen. There are a number of reasons why this should be followed, not least to provide a consistent approach to the evaluation of the protective system. In some cases, we are aware that less than the number of required thermocouples are used on the test specimen(s). While this is not in accordance with the standard requirements, the greater concern is there may be a part of the protective system that gets overlooked because of the reduced number of specimen thermocouples. Given that this test is only evaluated to temperature limits rather than the structural limits, it is imperative that all instruments are installed as required such that a representative sampling across the full test specimen is captured. Chapter 5 of the Standard is clear that 20 specimen thermocouples should be used per column. As with the furnace control matter discussed above, data produced using less than 20 thermocouples per column should be treated with caution and considered not compliant with the requirements of the test standard. 

Protective system

In all fire tests, the tested system should be representative of what will be used in the final installation on site. If changes are made to what was tested and certified, there will likely be an impact on performance. This means it is critical that the details of the tested system are recorded accurately and are then installed in practice as required in the certification documentation. If these details are not followed, there may be a loss of fire performance and a threat to life safety. 

For instance, in cases where a stainless steel wrap is added to columns for the test, even though it does not have a high thermal insulation value, the addition of the casing will add thermal protection to the steel column. It will do this by creating an air gap that insulates the column and by stopping the convection of hot gases in the furnace, which otherwise might have penetrated the protective system. This is just one example where a small element of the protective system, one that may appear to add little or no thermal resistance, can be critical to the system’s overall fire performance and proven by way of fire testing. Therefore the full configuration of the protective system, as tested, shall be installed on-site as well to help ensure the required fire safety levels are provided.

Durability

Often the protective products tested and certified to UL 1709 will be placed in harsh environments when placed in practice. It is for this reason that the Standard mandates durability testing that simulates these harsh environments be performed on all protection systems intending to be certified to UL 1709. The durability testing is conducted to UL 2431, the Standard for Safety for Durability of Fire Resistive Coatings and Materials, and the protection systems must comply with all requirements for Material Classification Category I-A: Outdoor, Heavy Industrial as prescribed in the Standard. The individual listing on UL’s Product iQTM database will indicate the protection system’s compliance with these durability testing requirements.

Conclusion

UL 1709 is increasing in its adoption. We believe this is the correct Standard to use to evaluate protective systems to structural steel for environments where a rapid rise hydrocarbon fire may occur. However, the test methodology and certification details must be followed to maintain the desired fire protection. Deviation from, or failure to comply with, the UL Certification requirements and individual design details will void the fire rating and UL Certification.

UL’s robust certification processes, which analyze how the test was conducted and what the tested specimen was comprised of before making a certification decision, provide a means of reassurance that the product and system covered by the UL Listing on Product iQ™ database complies with the specified requirements and will perform as intended and provide the necessary fire safety.

UL’s Structural Steelwork Fire Protection Guide:

Best practice for passive fire protection

We have created this guide to help code and inspection authorities, architects, contractors, installers, and other interested parties better understand the basic components of fire protection for structural steelwork.

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