DYNA

2.1. Clothing system

Two disposable and two reusable scrub and clean air suits were used in this study. All the clothing systems are currently used in operating rooms; all four are from different brands and have different materials/compositions. Table 1 shows the description of the studied clothing systems A and B. The clothing was stabilized in an adiabatic chamber before each test.

Table 1: Description of clothing system tested.

Source: The authors

2.2. Alambeta

Alambeta measuring device (Fig. 1) measures transient and steady state thermo-physiological properties [18], which simulates, during a very small initial contact, the heat flux between skin and fabrics. Alambeta measures thermal parameters like, thermal conductivity, resistance, diffusivity and absorbance. When the sample is inserted, the measuring head drops down, touches the fabrics, the heat flow levels are processed and thermo-physical properties of the measured samples are evaluated. The measurement lasts for several minutes only. This equipment test the objective evaluation of warm-cool feeling properties of fabric. To simulate the real conditions of warm-cool feeling evaluation, the instrument measuring head is heated to 32ºC, which correspond to the average human skin temperature, while the fabric is kept at the room temperature 22ºC. Similarly, the time constant of the heat flow sensor, which measures directly the heat flow between the automatically moved measuring head and the fabrics, exhibit similar value (0,07 sec), as the human skin. Consequently, the full signal response is achieved within 0,2 sec. [9]. Warm-cool feeling means the feeling we get when the human skin touches shortly any object, in our case textile. Since this feeling strongly affects the choice of people when buying the clothes or home textiles, the objective assessment of this feeling became very important [19].

2.2.1. Thermal conductivity (λ)

Thermal conductivity is a property of materials that expresses the heat flux that will flow through the material if a certain temperature gradient exists over the material.

The measurement result of thermal conductivity is based on the following eq. (1):

Figure 1: Alambeta equipment for thermal properties measurement

Source: The authors

The tested thermal properties are present in Table.2.

Table 2: Description of the tested thermal properties

Source: The authors

(1)

where:

P - heat power (W)

x - fabric thickness

A- area (m2)

ΔT- temperature gradient

The obtained results were treated statistically and the reproducibility of the different results, for each variable, was tested and analyzed.

Finally, selected softened samples of bed linen were evaluated by a dry thermal manikin to validate the conclusions.

2.2.2. Thermal diffusivity (a)

Thermal diffusivity is an ability related to the heat flow through the air in the fabric structure. The thermal diffusivity of the textile materials is the transcient thermal characteristic of textiles. It is expressed as eq. (2):

(2)

2.2.3. Thermal absorptivity (b)

The level of thermal absorptivity depends neither on the temperature gradient between the fabric and skin, nor on the measurement time.

Thermal absorptivity can be expressed as eq. (3):

(3)

where:

λ - thermal conductivity

ρ - fabric density

ς - specific heat of the fabric

This value just depends on the structure and composition of the material, particularly the surface properties. The lower the thermal absorptivity, the warmer the feeling during the short thermal contact of the skin with the fabric.

Since the thermal absorptivity is mainly the superficial property, its level can be changed by any superficial or finishing treatment, like raising, coating and softening [9]

2.3. Thermal manikin

The thermal insulation of clothing ensemble was measured using a thermal manikin, Fig. 2, with controlled skin surface temperature that simulates the wear. This thermal manikin, called “Maria”, is programmed to respond to the thermal environment as an average woman’s body; its size and configurations are similar to an adult woman. It is divided in 20 thermally independent sections and only sense dry heat transfer. Thermal manikin, positioned 0.1 m from the floor, was kept standing with their legs and arms held in vertical position without any motion. The skin temperature of all body was set, and during the test period maintained at 33 ± 0.1 °C. The tests were conducted in a climatic chamber where ambient conditions characteristic of an operating theatre were simulated, 20 °C ± 2 °C and 60% Rh. The climatic chamber can achieve temperatures around 15 °C to 35 °C and relative humidity around 35% to 85%.

Figure 2: Thermal manikin: photo of nude thermal manikin used on tests (a) and software body picture of thermal manikin and color legend of body segments temperature (b).

Source: The authors

Data acquisition started achieving stationary conditions after 60 min. During the acquisition period, the heat flux and the skin temperature of each body part record every minute. Thermal insulation ( ^_IT ) was calculated according to global method, eq. (4), where ^_Tsk [°C] is the mean skin temperature, T₀ [°C] is the room temperature, Q [W/m²] the sensible heat flux of the manikin and fi the relationship between the surface area of segment i of the manikin [20]. This is the general formula for defining the whole body resistance and the one that best fits the definition of thermal insulation expressed [12].

(4)

Furthermore, global method is less susceptible to significant variations to calculate thermal insulation. The global method should be used for calculating thermal insulation of clothing for all manikin control modes, especially for thermal comfort regulation mode [15]

The effective clothing insulation ( ^_Icle ), consisting of the difference between ^_IT and Ia are calculated by the eq. (5), considering ^_Ia is measured by operating the manikin nude.

(5)

For statistical data analyse the software “Action” was used. It was made the F-test of two variances at a 95% level of confidence. When p-value<0.05 then reject the two variances compared are equal.

3.1. Alambeta

Fig. 3 shows thermal properties of tested clothing. Thermal conductivity is a property of materials that expresses the heat flux that will flow through the material if a certain temperature gradient exists over the material [21]. Scrub suits have higher conductivity than CAS. SS B with 33% cotton in its composition has higher conductivity than polyester, that’s why SS B has higher conductivity than CAS D. Scrub suits have higher diffusivity than clean air suits. This property represents heat propagation velocity of material, so SS will diffuse the heat faster than CAS.

Figure 3: Thermal properties of clothing measured on Alambeta: condutivity (a), diffusitivity (b) and absoptivity (c)

Source: The authors

Figure 4: Heat loss from body section of manikin dressed with CAS (a) and SS (b).

Source: The authors

Thermal absorptivity is a warm-cool feeling parameter and represents instantaneous heat flow that appends when two bodies, with different temperatures, come into contact. This value just depends on the structure and composition of the material, particularly the surface properties. The lower the thermal absorptivity, the warmer the feeling during the short thermal contact of the skin with the fabric [19]. Single-use SS and CAS have the same absorptivity value and it is lower than for reusable SS and CAS. Each material that can absorb and conducts heat well, will remove the heat from the skin and make the user feels fresher [22].

3.2. Thermal manikin

Fig. 4 shows the heat loss from manikin body segments. According to Hensel cited in [21], the higher is the heat flux loss from the skin to the environment, the faster the temperature will drops and more intense is the freshness feeling. So a material that could absorb and conduct heat well, will remove heat from the skin and give the sensation of being a “coolest” garment. Hence, heat loss is closely related to thermal insulation, they are inversely proportional parameters. In this particular case, as expected, unclothed parts like feet, hands, forearms and face have higher heat loss.

Through heat loss values, total ( ^_IT ) and effective clothing thermal insulation ( ^_Icle ) can be calculated. In Fig. 4 can be seen that SS A have the lower thermal insulation, the difference between single use SS and CAS (A and C) is around 0,032 m².°C/W and for disposable ones (B and D) it is around 0,012 m².°C/W. However, the difference between SS and CAS is significant when we compare SS A with CAS C, and there is also a significant difference between scrub suits A and B.

Figure 5: Total thermal insulation and effective clothing insulation of scrub and clean air suits.

Source: The authors

Figure 6: Clo value of total thermal insulation of scrub and clean air suits

Source: The authors

Table 3: Statistically differences between clothing systems

Source: The authors

When the effect of air layer thermal insulation is removed ( ^_Icle ), clothing thermal insulation decreases but shows the same behaviour. For A suit, can be observed a decrease around 73%, about 58% and 57% for B and C, respectively, and 61% for D.

Thermal insulation of clothing can also be expressed in clo values, Fig. 5. The higher the value of clo, the greater is thermal insulation. Clo value of 1 is defined as the amount of clothing required to a human being at rest to be comfortable at room temperature of 21 °C [16]. The differences between clothing clo values are statistically significant (p-value < 0,05), except between suits B and C (p-value > 0,05), Table 3. So, the differences of wear SS B or wear CAS C can’t be perceived. SS A has the closest clo value of 1, meaning that for the user, the more thermal comfortable suit, according to clo value is SS A.