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Evaluation of thermal protective performance using full-scale dynamic manikin systems

In the earlier-mentioned test procedures, the manikins remain stationary, and the flame or hot water is directed onto the clothed manikin system at prescribed locations to evaluate the thermal protective performance. Hence, these procedures do not accurately simulate the firefighters’ activity at the site of a fire. These tests are also limited to garments and do not evaluate the thermal protective performance of other Personal Protective Equipment including helmet, gloves, boots, and self contained breathing apparatus (SCBA). In actual fire hazard scenarios, firefighters are active and move through thermal exposures. During this movement, different parts of the clothing may compress with firefighters’ bodies. At the point of compression, the air gap between clothing and firefighters’ bodies diminishes. This situation ultimately lowers the insulation property of clothing. It seems that use of a dynamic manikin system may provide a better understanding of clothing performance [334,365]. To date, dynamic flame manikin systems have not been fully explored to evaluate clothing performance.

Working principles of a few dynamic flame manikin systems: There is a dynamic flame manikin system available in Alden Research Laboratories [supported by the Navy Clothing and Textile Research Facility (NCTRF), and operated by faculty and students of Worcester Polytechnic Institute (WPI)] in Massachusetts to evaluate the thermal protective performance of firefighters’ clothing [334]. Additionally, DuPont also has a full-scale leg manikin system available, Thermo-Leg, to evaluate the thermal protective performance of trousers [365].

Alden Research Laboratories provides a facility to evaluate the thermal protective performance of clothing using a dynamic instrumented life-sized manikin system (Fig. 5.22). This movable manikin is constructed from fiberglass (its outer surfaces are coated with a high-temperature polymer) and can be equipped with up to 124 black-painted sensors. The experiment is conducted in a 2.4 m x 2.4 m x 3.6 m room, which is a modified ISO 9705 standard room [334,372,373]. This room comprises two doors (0.81 m x 2.4 m), one facing the other on two opposite walls. These two doors allow the manikin to completely pass through the room, without having to stop its motion inside the room. The movement of the manikin is controlled by a transverse chain driven track mechanism attached to the ceiling. The speed of the movement is monitored by a variable frequency drive (VFD) motor that comprises a forward/backward/off-switch to control the speed of the manikin up to ^0.9 m/s. In this test, the fire scenario is created by using the eight (30 cm) square-size propane torches, and the torches can be arranged in four different configurations to create four various fire scenarios: Configuration A applies even distribution of flames over the manikin’s surface; Configuration B provides intense radiation to the manikin, while limiting flame contact; Configuration C creates flashover conditions over the manikin and Configuration D represents wildfire scenarios with low flame heights up to the waist of the manikin. The torches are attached with a propane gas flow (0-70 g/s) controller to deliver a consistent and reproducible fire with accuracy within 1-3%. These torches can give an effective fire HRR in a range of 0-3.08 MW; however, for experimental purposes the average HRR can be set up to 1.6 MW. In this context, Woodward [372] measured the temperature and heat flux on the centerline of the flame at various locations of the room where the manikin’s sensors are expected to be during testing, and he concluded that Configurations A and C have the potential to expose the manikin to a heat flux of 84 kW/m2. Fay [373] also determined that a 1 MW fire can produce heat fluxes of at least 80 kW/m2 at a height ranging from 0.71 to 1.1 m of the room. During testing, sensors attached to the manikin can measure the amount of thermal energy transferred to the manikin (in unclothed and clothed conditions) from the fire scenarios to evaluate the time required to generate the second- and third-degree burns on firefighters’ bodies using a software package. In clothed conditions, the time to burn injury can be interpreted as the thermal protective performance of the clothing. Previously, this manikin system allowed for the application of jackets, pants, gloves, and boots with embedded sensors; recently, this manikin system has been upgraded for the application of helmet and SCBA, also with PyroCal sensors. It is noteworthy to mention that it is very difficult to maintain a constant heat flux in this type of testing. As a result, it is difficult to repeat the test. In the case of quick movement of the manikin, the sensors also may not get enough time to provide accurate performance readings. Presently, many sensors on this manikin are inoperable and need suitable replacements. It seems that this manikin system needs further development to properly evaluate the performance of thermal protective clothing.

Dynamic flame manikin of Alden Research Laboratories

Fig. 5.22 Dynamic flame manikin of Alden Research Laboratories.

Adapted from J.E. Sipe, Development of an instrumented dynamic manikin test to rate the thermal protection provided by the protective clothing (M.Sc. thesis), Worcester Polytechnic Institute, Worcester, MA, 2004.

Similar to the Thermo-Man discussed in Section 5.2.3, the Thermo-Leg was also developed by DuPont. This Thermo-Leg is used to evaluate the thermal protective performances of trousers [365]. The Thermo-Leg is a size 40 instrumented fiberglass- epoxy molded leg that simulates human running motion. The motion of the leg is designed based on biomechanical and kinesiology studies to simulate the path of the ankle of a running person. The Thermo-Leg can move at a frequency stride of 1.11 cycle/s (0.9 s/cycle) with an average stride length of 4.43 ft (1.35 m) and can produce a running speed of 9.8 ft/s (3.0 m/s). During this movement, a flame is administered to the leg from four large propane torches at a maximum heat flux value of 84 kW/m2. For the running motion spans of 5.5, 6.5, 7.5, and 8.5 s time intervals, the fire exposure can last for 3, 4, 5, and 6 s, respectively. As the Thermo-Leg is covered with 18 embedded sensors, it can measure the thermal energy transferred through the trousers. The measured thermal energy is used to calculate thermal protective performance in terms of time required to generate burn injuries. Although Thermo-Leg can contribute additional useful information regarding the impact of tested trousers’ material performance and design on thermal protective performance, more research is needed to validate the Thermo-Leg test protocol, to refine test procedures, and to develop guidelines for the analysis and interpretation of test results [334,365].

Assessment of thermal protective performances using dynamic flame manikin systems: Sipe [334] evaluated the thermal protective performance of PBI clothing using the dynamic manikin system of Alden Research Laboratories. The author evaluated the thermal protective performance of clothing in two positions: (1) when the manikin is stationary outside of the burn room, and (2) when the manikin is moving through the burn room. It has been identified that radiant heat predominates in the first position. However, when the manikin moves through the flame, a mixture of convective and radiant heat exposure predominates. It has been further identified that the clothing performance is greater when the test is carried out outside the room; the performance of the clothing was also higher in the case of quick movement of the manikin in comparison to the slow movement. This is because the intensity of thermal exposure is lower outside the room than the intensity of thermal exposure inside the room. Furthermore, Ellison et al. [374] evaluated the thermal protective performance of four different types of fabric-based clothing (A-D): fabrics of clothing A (100% Nomex outer shell, Goretex-laminated 100% Nomex moisture barrier, 100% Nomex quilt thermal liner), fabrics of clothing B (60% Kevlar/40% PBI outer shell, 100% Nomex moisture barrier, 100% Kevlar batt thermal liner), fabrics of clothing C (100% Nomex-IIIA outer shell, laminated Nomex moisture barrier, Sonatara E89 thermal liner), and fabrics of clothing D (100% wool outer shell, 100% cotton thermal liner). The clothing materials of A and B are very common for firefighters in North America; whereas, the clothing materials of C and D are mainly used by firefighters in Victoria, Australia. In this test, three different types of exposures at 1.5 MW were considered: (1) the manikin was stationary at the doorway of the burn room and exposed to fire for 30 s, (2) the manikin ran through the room at a speed of 0.27 m/s, and (3) the manikin ran through the room at a speed of 0.16 m/s. In this study, the thermal protective performance of the clothing was measured in terms of second-degree burn percentages on the manikin’s body as predicted by the sensors attached to the manikin. Clothing with second-degree burn percentages >10% on the manikin would not be recommended for use by firefighters, based on the medical profession’s definition of life-threatening burns. It has been found that all four clothing types possessed highest performance values in the case of exposure 1, whereas performance was lowest for exposure 3. Additionally, all four types of clothing generated <10% second-degree burns under the three different types of exposure; hence, they are all suitable for use by firefighters in actual fire hazards.

Behnke, Geshury, and Barker [365] evaluated the thermal protective performance of trousers made from inherently fire-resistant (Kevlar, Nomex) and chemically modified fire-retardant (Proban cotton, Zipro wool) fabrics. In the study, they evaluated the thermal protective performance at 84 kW/m2 using the Thermo-Leg developed by DuPont, and it was found that the performance of inherently fire-resistant fabrics-based trousers are higher than the performance of chemically modified fire- retardant fabrics-based trousers. They also compared the thermal protective performance values obtained from the dynamic Thermo-Leg manikin tests with the thermal protective performance values obtained from the stationary Thermo-Man manikin tests. Both tests used sophisticated heat sensors to provide substantial information on the performance of the trousers’ materials to protect against second- and third- degree burn injuries. It was found that the dynamic Thermo-Leg predicts more burns than the nonmovement legs in Thermo-Man. This is because the dynamic legs have less insulative air gap between the sensors and trousers in comparison to the nondynamic legs; as a consequence, the dynamic legs demonstrate more burns than the nondynamic legs. Additionally, the dynamic legs comprise more burns in between the knee and hip area because the back side of the heated trousers comes in direct contact with the sensors in this area and enhances the conductive transfer of heat to the sensors for generating more burns. In this study, it was inferred that the dynamic Thermo-Leg can more accurately simulate the actual thermal environments that are faced by running firefighters in a flash fire accident; however, the Thermo-Leg can represent only a part of the human body. It was also concluded from this study that it is necessary to maintain the strength and integrity of the garment in dynamic test configurations. As a lot of stretch occurs during movement, it is difficult to get a good thermal protective performance without maintaining the proper integrity of the tested garments.

 
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