Round robin study of total heat flux gauge calibration at fire laboratories

Pitts, William M.; Murthy, A V.; Ris, John L. de; Filtz, Jean-Rémy; Nygard, Kjell; Smith, Debbie; Wetterlund, Ingrid

doi:10.6028/nist.sp.1013

Cited by 11 publications

(15 citation statements)

References 2 publications

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“…Both the manikin and THF sensors used within this work were calibrated using primarily radiant heat sources, creating a discrepancy between the calibration environment and the application environment. The difficulties associated with the calibration of heat flux sensors to measure total heat flux in mixed‐mode environments have been acknowledged in the scientific literature . In 1999 NIST reported a method for calibrating against convective heat, and yet twenty years later it remains difficult to acquire sensors calibrated for both radiation and convection.…”

Section: Discussionmentioning

confidence: 99%

Thermal sensor performance and fire characterisation during short duration engulfment tests

et al. 2020

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A small-scale reproduction of the ISO 13506-1 thermal manikin was constructed to enable the assessment of manikin sensor performance, the partitioning of energy, and the variability of the fire generated during short duration heat and flame engulfment tests. The cylindrical test apparatus simultaneously housed four total heat flux (THF) sensors, one radiant heat flux sensor, and three manikin sensors.Calibrated manikin sensors were provided by nine laboratories and were categorised as buried thermocouple, copper-based, or surface-mounted thermocouple sensors.The test apparatus was exposed to fire generated by four propane torches for three exposure durations. All sensors presented similar profiles in net heat flux over time, which could be divided into four distinct phases: transient increase, pseudo-steady state, transient decrease, and post-exposure. Over pseudo-steady state, the mean THF over all exposure durations was 88 ± 8 kW/m 2 , and the ratio of convective to radiant energy was approximately 50:50, but highly variable. For a 4-second exposure, manikin sensors from five laboratories had a bias in heat flux greater than ± 5% during pseudo-steady state when compared with the THF sensors. This bias can primarily be attributed to the sensitivity of the manikin sensors to convective heat or heat loss due to sensor design. K E Y W O R D S calibration, convection, manikin, Protective clothing against heat and flame, radiation, sensor 1 | INTRODUCTION Thermal manikins are used to evaluate the performance of complete garments exposed to short duration heat and flame engulfment. 1 Sensors embedded within the manikins' surface (manikin sensors) record the change in heat flux directly or enable the calculation of heat flux through transient changes in temperature. From heat flux, the energy transferred through the test garment over a defined time period (ISO 13506-1), and the predicted skin burn injury (ISO 13506-2) are calculated. 1,2 The manikin sensors are expected to respond to the full range of heat fluxes (approximately 0-130 kW/m 2 ) and heat transfer modes which may be encountered during tests. Heat and flame engulfment is calibrated by exposing the nude manikin (without garment) to a mean incident heat flux of 84 kW/m 2 ± 5% across all sensors over the period of pseudo-steady state* (here forth referred to as manikin exposure calibration). The heat fluxes recorded under a garment are typically much lower than those encountered during manikin exposure calibration, and are influenced by garment composition and design, and exposure duration (3-12 s). *The ISO 13506-1:2017 standard currently defines pseudo-steady state as the 'steady region' of the heat flux curve.

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Section: Discussionmentioning

confidence: 99%

Thermal sensor performance and fire characterisation during short duration engulfment tests

et al. 2020

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“…It is known that Gardon and Schmidt‐Boelter gauges are not equally sensitive to convection. However, the 6.4‐mm air gap behind the fabric is a horizontally aligned enclosed space, and the air inside is stagnant and at the room temperature before the heat exposure.…”

Section: Experimental Methodsmentioning

confidence: 99%

Thermal response characteristics of fire blanket materials

et al. 2013

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SUMMARY The thermal response characteristics of over 50 relatively thin (0.15–3.7 mm) fire blanket materials from four different fiber groups (aramid, fiberglass, amorphous silica, and pre‐oxidized carbon) and their composites have been investigated. A plain or coated fabric sample was subjected to a predominantly convective or radiant heat flux (up to 84 kW/m2) using a Meker burner and a cone heater, respectively. In addition to conventional thermal protective performance ratings for protective clothing, two transient thermal response times (for the fabric back‐side temperature to reach 300 °C and for the through‐the‐fabric heat flux to reach 13 kW/m2) and a steady‐state heat‐blocking efficiency (HBE) were introduced for both convective and radiant heat sources. For most woven fabrics, the HBE values were approximately 70 ± 10% for both convection and radiation and only mildly increased with the fabric thickness or the incident heat flux. Nonwoven (felt) fabrics with low thermal conductivity exhibited significantly better insulation (up to 87%) against convective heat. Highly reflective aluminized materials exhibited exceptionally high HBE values (up to 98%) for radiation, whereas carbon and charred aramid fabrics showed lower HBEs (down to 50%) because of efficient radiation absorption. A relatively thin fire blanket operating at high temperatures can efficiently block heat from a convective source by radiative emission (enhanced by its T4‐dependence and high surface emissivity) coupled with thermal insulation and from a radiant heat source by surface reflection while the aluminum surface layer remains. Copyright © 2013 John Wiley & Sons, Ltd.

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“…diameter, bare-bead, Chromel-Alumel (type K) thermocouples while Schmidt-Boelter gauges were used to measure total heat flux. Results from an international study on total heat flux gauge calibration and response demonstrated that the uncertainty of a Schmidt-Boelter gauge is typically ± 8% [18]. The first heat flux gauge were installed 1.01 m on center from the side wall of the structure.…”

Section: Instrumentationmentioning

confidence: 99%

Impact of Flashover Fire Conditions on Exposed Energized Electrical Cords/Cables

2019

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There has been prior research exploring the exposure of common electrical cords and cables to fire, but that has traditionally been at the lab scale and under near steady-state exposures. The goal of these experiments was to expose six types of cords and cables in a room-scale compartment with a fuel load sufficient to drive the compartment through flashover. The basic test design was to expose the cords and cables on the floor of a compartment to a growing fire to determine the conditions under which the cord/cable would trip the circuit protection device. All of the cords were energized and installed on a non-combustible surface. The six cables and cords were protected by three different circuit protection devices which were remote from the thermal exposure. This configuration resulted in 18 exposures per experiment. The room fires experiments consisted of three replicate fires with two sofas as the main fuel source, two replicate fires with one sofa as the main fuel source and one fire with two sofas and vinyl-covered MDF paneling on three walls in the room. Each fuel package was sufficient to support flashover conditions in the room. The average peak heat release rate of the sofa fueled compartment fires with gypsum board ceiling and walls prior to suppression was 6.8 MW. The addition of vinyl covered MDF wall paneling on three of the compartment walls increased the pre-suppression peak heat release rate to 12 MW. In each experiment during post flashover exposure, the insulation on the cords and cables ignited and burned through, exposing bare wire. During this period, the circuits faulted. Assessments of both the thermal exposure and physical damage to the cords did not reveal any correlation between the thermal exposure, cord/cable damage, and trip type.

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Round robin study of total heat flux gauge calibration at fire laboratories

Cited by 11 publications

References 2 publications

Thermal sensor performance and fire characterisation during short duration engulfment tests

Thermal sensor performance and fire characterisation during short duration engulfment tests

Thermal response characteristics of fire blanket materials

Impact of Flashover Fire Conditions on Exposed Energized Electrical Cords/Cables

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