Study on testing and evaluating technology of flame resistant clothing

Yuhong Chen

The Quartermaster Research Institute No.69 Lumicang Street, Dongcheng District, Beijing, P.R.China, 100010+8610   66727212/yuhong810@yahoo.com.cn

ABSTRACT

The flame resistant clothing is the basic equipment for firefighter. The main functions of flame resistant clothing are to resist flash fire and radiation damage, and keep safety and health of firefighter. This paper describes the flash-fire manikin system developed by the Quartermaster Research Institute, which can be used to estimate area percentages of the second-degree and third-degree burn injury caused by the flash fire and evaluate the flame resistant protective performance of clothing by simulating the heat transfer process among human body, clothing and fire environment.

Keywords:

Flame resistant clothing, Manikin, Test, Evaluation

INSTRUCTIONS

The flame resistant clothing is the basic equipment for firefighter. The main function of flame resistant clothing is to resist flash fire and radiation damage, and keep safety and health of firefighter. It is mainly used vertical combustion test method, limiting oxygen index method, TPP (Thermal Protective Performance) method and RPP (Radiant Protective Performance) method to test and evaluate flame resistant performance of clothing[1.2]. These methods can only be used to evaluate the protective performance of textile materials but not to mimic overall protective performance when wearing clothing. With the development of manikin, the technology of testing and evaluating flash-fire manikin attracts more and more attention abroad, and the flame resistant clothing and determining the flame resistant performance of clothing through estimating the second-degree and third- degree burn injury caused by the flash fire by simulating the heat transfer process among manikin, clothing and fire environment. This paper describes the flash-fire manikin system developed by The Quartermaster Research Institute and its application. This testing result will provide the important information for the research and design of firefighter clothing.

METHODS

1 Structure and function of system

The system mainly includes manikin system, fuel and delivery system, control system, data acquisition system and computer software system (Fig.1).

Fig.1 Structure of System

Manikin system: An upright manikin is similar to an adult male human in the shape and size. The manikin should be constructed of flame resistant, thermally stable, nonmetallic materials. About 120 heat sensors are distributed as uniformly as possible in each area on the manikin surface (Fig.2).

Fig.2 The distribution map of the sensors on the surface of manikin

Fuel and delivery system: It consists of fuel supply, delivery and burner system to provide reproducible flash fire exposures[7][9].

Control system: It can control the pressure of the delivery piping, duration of flash fire exposure, ignition procedure and related safety equipments.

Data acquisition system: It can acquire and store the results of the measurement from 120 sensors and communicate with computer by data bus.

Computer software system: It can receive the output of the sensors, calculate the heat flux and predict the burn injury level of the exposure. It also can monitor all the status of related equipment.

2Skin heat transfer model and burn injury assessment

2.1Characteristic of skin burn injury

When human exposes to fire, the skin burn injury degree depends on two factors: one is the heat flux of fire, the other is exposure duration. Lot of materials showthat, when the temperature of skin is at 44℃ , it takes about 3h when the non- recovery burn injury occurs. While the temperature of skin reaches 70℃ , the non-recovery burn injury occurs immediately. In order to prevent from second-degreeinjury occurring, the skin temperature must be below 62℃ if exposure duration is 3s. While the duration is 6s, the skin temperature must be below 59℃ . Therefore, when the temperature is above 44℃ , skin burn injury may occur[3-5]. The duration-skin temperature curve is shown in Fig.3.

Fig.3 temperature-duration curve of skin burn injury

2.2Skin heat transfer model

In order to calculating the skin temperature of different depth, the thermal wave model of bioheat transfer(TWMBT) is applied[6.8.10]. This model is as follow:

Ñ ·[KÑT (r, t)] + [WbCb(Tb - T ) + Qm + Qr +t (-WbCb ¶T¶t

+ ¶Qm +¶t

¶Qr )]¶t¶2T (r, t)= rC[t ( ) +¶t2

¶T (r, t) ]¶t

（1）

Where, -density of blood [kg/m3], -specific heat of blood [J/kg. ℃ ], -

specific heat of tissue [J/kg. ℃ ], T- tissue temperature [℃ ], -artery temperature

[℃ ], t-time [s], -thermal conductivity of tissue [W/m. ℃ ], -blood perfusion

rate [kg/m3.s],   and - volumetric heat due to metabolism and spatial heating

[W/m3], and -thermal relaxation time[s].

2.3Skin burn evaluation model

The total skin burn damage can be evaluated by following model:

t -DE

W = ò Pe RT dt0（2）

Where,

Ω-a quantitative measure of burn damage at the basal layer or at any depth in the dermis,

P - frequency factor, s–1,e - natural exponential = 2.7183,

E - the activation energy for skin, J/mol,

R - the universal gas constant, 8.315 J/kmol · K,

T - the absolute temperature at the basal layer or at any depth in the dermis, K, andt - total time for which T is above 44°C (317.15 K).

If Ω is less than, or equal to 0.5, no damage will occur at the basal layer. If Ωis between 0.5 and 1.0, first-degree burns will occur, whereas if Ω>1.0，second- degree burns will result. Mathematically, a second-degree burn injury has been defined as Ω>1.0 at the epidermis/dermis interface, a third-degree burn injury has been defined as Ω>1.0 at the dermis/subcutaneous interface[11-13].

RESULTS

Tests of flame resistant clothing

Three kinds of 100% cotton and a cotton-polyester flame resistant clothing are selected as test specimens. The fabric flame resistant performances of these specimens are afterflame time ≤5s, afterglow time ≤5s and damage length≤150mm. These specimens are the same size and style. Exposure time is 4s. Thetest results are show in Tab. 1.

Tab. 1 Test results

For the three kinds of 100% cotton specimen, the thicker the fabric, the smaller the third-degree burn injury area and total burn injury area in table 1. These results illustrate that the thicker clothing will provide better flame resistant protective performance. For the CVC specimen, the percentage of the third-degree burn injury area and total burn injury area are the smallest. These results illustrate that the CVC clothing will provide the best flame resistant protective performance among these clothing.

Tests of flame resistant protective performance of different style clothing  In order to study the impact of clothing styles on the flame resistant protective performance of protective clothing, we select two kinds of flame resistant protective clothing which are made of same fabric but of different style. One is open in the hem of clothing (Clothing 1). The other is jacket style (Clothing 2). The exposure time is 4s. The test results are shown in Tab. 2.

Tab. 2 Test results of different style clothing

In Tab. 2, the results show that the burn injury of Clothing 2 is less than that of Clothing1. The flame resistant protective performance of Clothing 2 is much better than that of the Clothing 1. By analyzing the test process record, it is found that the fire get into the inner of the clothing1 from the bottom of the clothing because it is very loose in the bottom and inner. So it continues to burn for 3s when the flash fire is extinguished. These results show that the style of clothing has very important influence on the flame resistant protective performance of clothing. Therefore, we should take into account the design of the open part of clothing.

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