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'NEED AND IMPORTANCE OF USING TESTED AND LISTED FIRE-STOP SYSTEMS’ IN BUILDINGS

almost 4 years ago

Authored by Gaurav Srivastava, Associate Professor, Civil Engineering, IIT Gandhinagar

IIT Gandhi Nagar

1.7K

‘Need and importance of using Tested and Listed firestop systems’ in buildings


Gaurav Srivastava

Associate Professor, Civil Engineering, IIT Gandhinagar

 

Compartmentation is a key idea that prevails in the field of fire safety of buildings. If implemented properly, it ensures that a fire remains small in size and localized in space. It is an important component of the egress system of a building, e.g., compartmentation of the fire exit stairwell. Partition walls and fire doors are well-known components of a building that play a crucial role in its compartmentation strategy. The fire rating requirements (with respect to a standard fire curve) of partition walls and fire doors are typically specified in terms of three characteristics:

  • load resistance (R): time up to which the component can resist the service loads (applicable to load-bearing members only),
  • integrity (E): time up to which the component does not allow the passage of hot gases or flames to the unexposed side, and
  • insulation (I): time up to which the temperature on the unexposed side of the member remains below a pre-defined threshold (usually 140 °C).

The lowest of R, E and I is considered the fire rating of the component being tested. Figure 1 shows the standard fire curve vis-à-vis a time-temperature curve for a typical real compartment fire.


Figure 1: Standard and real fire curves. Standard fire captures the post flash-over behaviour of a typical compartment fire [1].


In all buildings, there are multiple services such as electrical conduits and water/drainage pipes that run across floors or across compartments. These service crossings have the potential of compromising the fire rating of the larger component. Imagine a scenario where a plumbing pipe melts during a fire and creates a gap in the floor through which hot gases and flames can pass (even though the E rating of the floor has not been surpassed). Moreover, buildings with façade systems may have inherent gaps at the floor-façade connection by design. The NBC 2016 Part 4 recognizes such scenarios and specifies the following:

Cl. 3.4.6.1: The electrical distribution cables/wiring shall be laid in a separate shaft. The shaft shall be sealed at every floor with fire stop materials having the same fire resistance as that of the floor.
Cl. 3.4.10.2: All gaps between floor-slabs and façade assembly shall be sealed at all levels by approved fire resistance sealant material of equal fire rating as that of floor slab to prevent fire and smoke propagation from one floor to another.

These clauses introduce a new term ‘fire stop material’ or simply ‘firestop’. Firestop refers to a mechanism that is used to seal the gaps that exist (such as at floor levels in an electrical shaft) and that may be created during a fire (such as due to melting of a plumbing pipe) in a fire barrier of a building. Although the NBC 2016 specifies that the firestops should have the same fire rating as the fire barriers, it does not specify the test methods. One may refer to standards such as ASTM E814, ASTM E2307, or UL 1479 for discussions on the testing methods to determine fire ratings of firestop systems. Typically, it is specified in the following terms: F rating (broadly similar to E rating discussed earlier) and T rating (same as I rating discussed earlier). While these ratings provide a fair measure of the performance of a firestop system, the author believes that the ability of a firestop system to stop smoke from passing through is more critical from a life safety perspective. A ‘smoke rating’ is required to assess this capability of the firestop system. While none of the existing standards give a testing method or measure of smoke rating, the so-called L rating [2], which is an air leakage rating (and hence crudely indicates smoke leakage), can be utilized.

An L rating is a measure of the rate of air leakage per unit area of the firestop system (m3/s of air leaking per m2 of the firestop system) at a pressure differential of 75 Pa (7.4x10-4 atm) at ambient temperature as well as at an elevated temperature of 204.4 °C (400 °F). The testing is done at two temperatures to assess air infiltration under cold as well as hot conditions. It is well-known that in a real fire scenario, the temperature of hot gases can easily reach 850-900 °C and hence, use of the L rating to assess smoke ingress through a firestop system can be questioned. Moreover, in case of façade systems, movement of the transoms and mullions during a fire, termed as hot movement, can further enhance the chances of smoke ingress through the firestop system.

The fire at the ESIC hospital Mumbai, that claimed 13 lives and left over 100 injured, is a documented case of how the use of inadequate firestop mechanisms led to a massive tragedy. The case of fire at the Grenfell tower of London, where the air cavity between the insulation and the curtain wall took the centre stage in aiding rapid spread of fire that quickly engulfed the entire building, is also well-documented. It is clear that well-designed and properly tested firestop systems can be the difference between life and death in the event of a fire. While the aforementioned testing standards can be used to differentiate between adequate and inadequate firestop systems, assessment of the performance of firestop systems in real fire scenarios remains challenging.

To understand the real-life performance of firestop systems, multiple full-scale fire experiments have been conducted at IIT Gandhinagar. It was found that a properly tested (rated) firestop system aided in maintaining tenable conditions in the adjoining compartments throughout the fire duration while an unlisted firestop system caused rapid ingress of hot gases and high temperature in the adjoining compartment within three minutes of the ignition. In another experiment comparing two different rated firestop systems, it was found that the levels of carbon dioxide and carbon monoxide gases in the adjoining compartment were two to three times higher in one system vs. the other. This clearly highlighted the importance of a smoke rating for such systems.

As we continue to build high-rise buildings where external firefighting becomes challenging, our dependence on the inherent firefighting mechanisms of the building (and hence compartmentation) has increased tremendously. Thus, having a properly tested and adequately designed firestop system as part of the building’s passive fire protection system is crucial. Some general guidelines that can be used to assess the adequacy of the firestop system are summarized below:

a.      Firestop system: It is to be noted that throughout the article, the term ‘firestop system’ has been used to emphasize that to ensure compartmentation, a number of different components must come together a system. Rating of the entire system is of importance (weakest link in the chain determines the overall strength).

b.      Is the firestop system properly tested: Designers should resort to ‘listed’ systems (e.g. by Underwriters Laboratories, Factory Mutual, etc.) to ensure that the system they are using has been properly tested by a trustworthy laboratory. In case a non-listed system is to be used (e.g. due to design requirements), designers may request reports of tests conducted at standard laboratories (accredited by UL or FM, etc.) to ensure that the desired requirements are being met. In view of point (a) above, test methods that consider entire systems are to be preferred over those which test individual components.

c.      Is the firestop system adequately designed: Design conditions of one building may differ completely from that of another building and hence, it is important to consider these with respect to the test procedures used by different standards. The designers should assess how close are the real conditions to the test conditions. In case of significant deviations, additional testing or engineering judgement can be used based on the opinion of an expert.

d.      Documentation: All firestop systems used in a building should be properly documented in the form of test reports, listing details, product specifications and inclusion of the installation details in the building drawings (both plan and elevation). These documents have an important role throughout the life of the building.

e.      Inspection during installation: It is important to have a close watch on the materials and methods being used during the installation of firestop systems to ensure that the system being installed is as per design. One advantage of using listed systems is that the product manufacturers are liable to install the system as per the listing requirements and the on-field engineer need not have full knowledge of the installation requirements.

Once installed, firestop systems require periodic inspections to assess their adequacy from time to time. The documentation regarding firestop systems for a particular building serves as an important reference point for such inspections and greatly helps the inspector in assessing the adequacy of firestop systems. Local bylaws or building codes may require more thorough inspections (depending on the importance, occupancy, location or height of a building). These can be non-intrusive (visual) or intrusive (requiring destructive testing) depending on the situation. A detailed guide on inspection can be found on the web [3].

 

[1] Chandrasekaran, S. and Srivastava, G., Design Aids of Offshore Structures under Special Environmental Loads Including Fire Resistance, 2018, Springer, ISBN: 978-981-10-7607-7.

[2] UL 1479, Standard for Fire Tests of Penetration Firestops.

[3] Inspection Guidelines for Penetration Firestop Systems and Fire Resistive Joint Systems in Fire Resistance Rated Construction – 5th Edition. URL: https://www.firestop.org/inspection-guidelines.html, accessed on 14th April 2020.


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