The Impact of Extreme Fire Behavior on Firefighter Escape Systems International Technical Rescue Symposium November 3-6, 2016, Albuquerque, NM Mike Forbes, RopeCraft Matt Hunt & Josh Walls, Sterling Overview This testing was to address how the anchor end (hook and rope) of an escape system performs when subjected common fire conditions present during a residential structure fire. A device was designed and built to simulate a fire room that allowed 2 loaded escape systems to be anchored independently at various locations in the room. The systems would then be subjected to fire conditions such as rollover and flashover for a set period of time or until failure of a component occurred. Background Firefighter escape systems have been available in various forms for years, from a simple length of rope stored in a pocket, to more elaborate systems, with the intent of providing an option of last resort for firefighters trapped on floors above ground level. In 2005 FDNY began to research providing dedicated escape systems for each firefighter to carry while on duty. They settled upon a device, rope, and escape hook. The concept was that the firefighter could utilize this hook in various ways and to create an anchor by which they could then exit the structure and rappel to safety. The hook was created of cast steel, the rope of Technora, and the device a variation on the Petzl GriGri design. A variation of this system was then brought to market commercially as the Petzl EXO. The materials chosen for the system were chosen based on their ability to survive fire conditions the firefighter might encounter. The hook was made of steel because it has a higher melting temperature than what might be expected, and the rope utilized Technora as it is a fiber that can resist heat exposure in excess of 900 F without failing. Following the introduction of the Petzl EXO, other systems came onto the market made by various manufacturers utilizing different ropes, hooks, and descent control devices. Some of these products used different fibers for the rope and some used aluminum for the hook, in an attempt to lighten the overall weight of the equipment. Fire escape ropes are evaluated for their resistance to temperature through a controlled test utilizing an oven with a load applied at various
temperatures (NFPA 1983 - Elevated Temperature Rope Test). This test does not subject the ropes to actual fire conditions 1. Escape hooks are not evaluated for temperature resistance, only tensile strength, yet they have the potential to be subjected to the same high temperatures and conditions as the ropes. If flashover can create temperatures greater than 1112 F, Aluminum (7075-T6) melts between 890-1175 F, and Technora decomposes at 932 F then the following questions should be asked: The Device Will the system survive a flashover? Does steel or aluminum offer a significant benefit or drawback? What is the weakest link in the system? What about the stitching on the sewn eye? The device attempts to simulate real world conditions found in a fire room during rollover and flashover. It allows for the anchor end of the escape system, the rope and the hook, to be anchored at various locations inside with a static load applied simulating a firefighter hanging from the rope. The enclosure simulates a scaled down residential bedroom with an adjustable window opening. The device will allow for two hooks and ropes to be simultaneously tested during each cycle. This allows for a comparison to be made between differing materials if desired. All attempts were made to create the same fire conditions between tests and subject the test samples to similar conditions. Structure Frame: Square steel tubing structural supports to support the test masses. Walls: 36 x 36 x 24 steel angle iron and sheet metal with seams caulked with high temperature sealant. Window: 12 H x 16 W with removable inserts that reduce the opening in order to change the fire conditions. 2 metal doors, left and right, to allow for loading fuel and test samples. Left door has adjustable air damper to control air flow. Floor: Fire brick on top of steel sheet. The fire brick is only present where the fuel is located. Anchor Points Window Sill: Plate steel, 6 deep, with a replaceable, sacrificial wood apron that allows the tip of the escape anchor to penetrate approximately 0.25. 1 NFPA 1983:2012ed. - 7.11.6.1 This test shall be conducted at two independent conditions and shall have a minimum time to failure of 45 seconds at 600 C while holding 300 lb and of 5 minutes at 400 C while holding 300 lb.
Remote anchor: 2 round schedule 40 steel pipe, welded in place horizontally 2 above the floor. Fuel Kiln dried Douglas Fir. In order to create a consistent fuel package, layers of wood oriented in the same manner was created. Each layer consisted of eight 1.5 x 16 x 0.375 slats connected together by 1 staples with an 8 long slat joining them together. Weight/layer: 1.316 lb (597 g). The bottom layer was created with 2 slats creating a spacer for the ignition material. Weight: 0.445 lb (202 g). The layers were stacked vertically with approximately 0.25 offset to create the most rapid fire growth. The fuel was ignited by lighting 8 loosely wadded 8 x10 newsprint bundles placed within the spacer layer under the main fuel package with a small propane torch. Test Masses 300 lb masses constructed of cast and plate steel with chain to allow for the mass to be varied. One mass (M1) hangs directly below the window sill and the other (M2) inline and toward the rear of the device. In order for M2 to apply tension to the sample in the same location as M1, a series of pulley blocks were installed to route the rope correctly. Since this routing changes the amount of friction, thereby changing the tension the anchor receives, M2 was increased to ensure equal tension was applied to both test samples. Calibration tests were conducted with a load cell affixed to each anchor until the force was equal. Data Acquisition 4 thermocouples were installed. They were placed at the sill (inside between the hooks), top of window, at the remote anchor, and 0.5 below the ceiling. All thermocouples were K-type, 100-1250C, with a 5mm diameter probe. Data was acquired by using an Arduino Uno micro-controller coupled with individual thermocouple amplifiers. Sample rate was 1 Hz. Data was exported to Microsoft Excel for analysis. Thermocouples were calibrated prior to use by testing with ice and boiling water as references. Imaging High definition video from outside of the window was recorded for most tests. Still photos were also taken to document the test process/results.
Fire Conditions The goal was to create realistic fire conditions that the fire service could potentially experience. Temperatures obtained in the device (>1200 F) are equivalent of those obtained from previous studies 2. The device is able to recreate rollover and flashover conditions found in common compartment fires. Tests The escape anchors evaluated were the Crosby and Sterling Lightning GT. The majority of the hooks were used, however all showed minimal wear and were all in excellent, serviceable condition. The primary rope evaluated was Sterling FireTech2, 7.5mm, 100% Technora sheath/core escape rope. 2 tests were conducted with Sterling PER, 8mm, 100% Nylon rope as a comparison to Technora. The hooks were attached to the Technora rope by a factory-sewn termination by Sterling, utilizing Technora thread. All samples were given a unique ID number and marked accordingly. A total of 18 samples were tested, 11 in the remote anchor configuration and 7 at the sill. All tests were conducted outdoors at a rural location near Moscow, Idaho on 6/27/16 and 07/06/16. The test location was sheltered from the prevailing wind however a mild breeze could be felt at times during some of the tests. After fire testing was complete all of the samples were sent to Sterling for static pull failure testing. The ropes and hooks were tested according to NFPA 1983:2012ed - Anchor Devices. The hooks were tested without lateral support which allows for out-of-plane bending to occur. If the hook failed before the rope, the rope was then tested with a 0.5 pin through the sewn eye. 2 Peacock et al., Defining flashover for fire hazard calculations, Fire Safety Journal 1999: 332.
Conclusions No failures occurred prior to 9 minutes during any test. If a failure occurred, the rope was the primary failure point 3. Remote anchors failed sooner than sill anchors. One potential explanation for this is they are exposed to more heat and direct flame impingement than at the sill. When a remote anchor failed, the rope was always the failure point. No Technora ropes failed when the hook was anchored at the sill. No steel hook failed in any configuration and there was no evidence of structural compromise. Aluminum hooks can begin to twist in the remote anchor configuration, however no hook failures occurred in this position. The aluminum hooks with highest heat exposure failed at an average load of 12.655 kn (n=4). New Lightning GT hooks failed on average at 17.3 kn (n=3). This is a reduction of 26.85%. NFPA 1983 specifies an MBS of 13.5 kn for an anchor device. The annealing temperature for 7075-T6 aluminum is 412C (775F). The significant yielding that occurred during testing of the samples and significant reduction of strength leads us to believe that the hooks were partially annealed as a result of the high temperature exposure. 2 Crosby hooks were tested and both released from the anchor prior to failure making a strength comparison between aluminum and steel hooks difficult to make. A slightly higher yield strength (25.0 kn vs 23.6 kn) was noted on the non-heated hook. Results General Observations For tests 1-4, 6 fuel layers were used and there were no failures recorded. The fire conditions were such that rollover and flashover did occur and temperatures in excess of 1200 F were recorded. For tests 5-8, the fuel package was increased to 10 layers in order to increase the time the samples were exposed to high temperatures and extreme fire behavior. With this increase in fuel, although temperatures did not increase, came failures of the rope and one release of a hook from the sill. 3During test #7 a hook released from the sill. It is difficult to determine the cause of this release. The tip was dulled possibly from thermal exposure and/or contact with the steel sill. More testing is warranted to pursue this failure mode.
During all tests, whether a failure occurred or not, the Technora rope became very stiff and brittle where it was exposed to high temperatures and/ or direct flame contact. Test Hook 1 ID Hook 2 ID Loc1 Loc2 Rope Fuel MBS 1 MBS 2 1 GT 1 Crosby 2 RA RA FireTech2 6 11.6/14.5 N/A 2 Crosby 3 GT 4 RA RA FireTech2 6 78 24.7/15.89 3 GT 6 Crosby 7 Sill Sill FireTech2 6 24.74/10.83 N/A 4 GT 7 Crosby 8 Sill Sill FireTech2 6 21.94/14.52 N/A 5 GT 9 Crosby 10 RA RA FireTech2 10 2.54/12.69 N/A 6 Crosby 11 GT 12 RA RA FireTech2 10 N/A N/A/12.39 7 GT 13 Crosby 14 Sill Sill FireTech2 10 25.26/13.12 N/A 8 Crosby 15 Crosby 16 RA Sill PER 10 N/A N/A 9 GT 17 Crosby 18 RA RA FireTech2 12 N/A/12.42 Released at 23.6 kn TABLE KEY Test Test ID # Hook 1 Hook on left side of device ID Hook ID Hook 2 Hook on right side of device Loc-1 Anchor location of Hook 1 (RA=Remote Anchor) Loc-2 Anchor location of Hook 2 Rope Rope type Fuel Number of layers of fuel. Does not include the spacer. If >6 than the fuel split between 2 equal stacks MBS 1 MBS in kn (Rope/Hook) MBS 2 MBS in kn (Rope/Hook) Note: Only 2 Crosby hooks were tested (18 & Control). Before failure would occur the hook tip would release from the fixture due to bending in the saddle. The release occurred at forces greater than 23 kn for both tests.
FUEL = 6 LAYERS Observations: Discoloration of both hooks. Anodizing of GT would become rough to touch and Crosby paint would bubble and darken. Rope becomes stiff and brittle. During failure testing all hooks yielded significantly releasing from the anchor without any fracturing of material. POST HEAT EXPOSURE POST STATIC FAILURE TESTING POST HEAT EXPOSURE
FUEL = 10-12 LAYERS Observations: Discoloration of both hooks. Anodizing of GT would burn completely off and Crosby paint would bubble and darken. Rope becomes stiff, charred, and brittle. Failures of rope occurred in remote anchor configuration during tests 5,6, and 9. During failure testing, aluminum hooks failed on average at 12.655 kn (n=4,std=0.338) POST HEAT EXPOSURE POST STATIC FAILURE TESTING POST HEAT EXPOSURE