TPP thermal protection performance tester test analysis

Protective clothing is one of the most widely used varieties of protective clothing, which can protect the human body from heat damage. The fire scene where firefighters work is not a dry environment, especially when firefighters put out an open flame, the human body will sweat a lot, and the clothes inside will absorb a lot of sweat from the human body, and the fire-fighting water can also be transferred to the inner layer through the outer surface of the clothes . These water evaporates into water vapor at high temperature, and transfer to the surface of human skin, which will burn human skin. Therefore, it is of practical significance to study the thermal protection performance of wet fabrics.

Experimental section.

 

Test materials

 

The structure of a fire suit is generally divided into four layers, consisting of an *outer layer, a waterproof and breathable layer, an insulating layer and a comfort layer. From the various layers of aesthetically pleasing materials suitable for firefighting suits, one is chosen as the experimental fabric to compare the change in thermal protection performance of the different layers of materials after moisture absorption.

 

Test Method

 

The TPP value reflects the fabric's ability to provide thermal protection against the combined effects of thermal radiation and thermal convection. The greater the value, the better the thermal protection performance of the thermal protection garment; conversely, the worse the situation. The test is carried out by placing the sample horizontally on a specific heat source. At a defined distance, the heat source appears as two different forms of heat transfer - thermal convection and thermal radiation. A copper heat flow meter placed on the other side of the sample measures the temperature at the back of the sample. The flame is required to come into direct contact with the sample so that the heat flow reaching the fabric surface reaches 84 kw/m2. The heating curve is measured with the copper heat flow meter on the back of the sample and compared with the Stoll standard curve to obtain the time t required for the secondary burn and multiplied by the exposed heat energy q to obtain the TPP value. It is calculated as TPP = 2 x q type:q is the prescribed radiant heat flux (84kw/m2);t:s. TPP experiments were carried out using a TPP thermal protection performance tester, according to NFPAl976 standard.

 

The samples were divided into 5 groups, numbered l~5. Each group consisted of 4 fabrics, A.B.C.D. Three samples were taken from each group and each sample was placed in a sealed plastic bag. The first group was the comparison group and no water was added. Group 2 to 5 samples were sprayed with 5.10.15.20ml of water evenly using a spray bottle. The moisture absorbing samples were left to stand in a constant temperature and humidity environment (20°C and 65% relative humidity) for 24 hours to allow the samples to fully absorb water. The TPP value of the sample after moisture absorption was measured using the TPP test and the average value per tissue was the TPP value of the sample.

 

TPP Thermal Protection Performance Tester tests single layer fabrics for moisture and thermal protection analysis.

 

Experimental results:

 

① Effect of moisture content of single-layer fabric on thermal protection performance. Among the four fabrics, the moisture content of fabric B is less than 3%, basically no change compared with that before moisture absorption. Therefore, the secondary burn time and TPP value of fabric B after moisture absorption did not change much compared with those before moisture absorption. This is because the B fabric is a polytetrafluoroethylene film, which is a waterproof and breathable fabric with excellent performance. There is basically no condensation on the surface, so the water content is very low. Because the flame-retardant cotton fabric D of the comfort layer has good water absorption and the highest water content, the outer layer fabric A is second, and the heat insulation felt C is the medium moisture absorption layer. The hygroscopicity of the three-layer fabric increased with increasing moisture, and the secondary burn time and TPP value increased with increasing moisture content. The moisture content of the monolayer fabric has a high positive correlation with the secondary burn time and TPP value. The higher the water content, the greater the TPP value of the fabric, and the corresponding time for the skin to reach the second burn will be prolonged. Therefore, the effect of water content on TPP is basically the same as that of the second burn time.

 

②The linear regression model of TPP value and second burn time took TPP value and second burn time as variables, water content as regression independent variable, and SPSS software established a linear regression model.

 

The unary linear regression model of TPP value and water content is TPP value=10.732+0.072×water content, and the unary linear regression model of second burn time and water content is second burn time=5.164+0.062×water content.

 

Experimental results:

 

The water content of the single-layer fabric has a significant relationship with the secondary burn time and TPP value, and there is a significant linear regression relationship between the secondary burn time and IPP value and water content. When the water content increased by 1%, the secondary burn time was prolonged by 0.062s, and the TPP value increased by 0.072kJ/cm2. The secondary burn time and TPP value increased with the increase of water content. Under the combined heat transfer conditions of strong radiation and convection (82.21kw/m2), water helps to improve the thermal protection performance of single-layer fabrics. The higher the moisture content, the greater the thermal protection of the single-ply fabric. Under standard conditions, the thermal protection performance of water-containing fabrics is better than that of dry fabrics. In this case, the moisture in the fabric will evaporate quickly, and the later the radiation and convection heat transfer to the back of the fabric, the steam will take away part of the heat and reduce the heat reaching the human body, thereby improving the thermal protection performance of the single-layer fabric. The higher the moisture content, the more moisture evaporates, the more heat is taken away, the faster the heat dissipation, and the stronger the thermal protection performance of the fabric. This conclusion applies to cases where the water content is less than 50%.