BOX TEST
This part of the standard indicates the procedure for testing heat and flame resistant materials and clothing when there is a risk of electric arc using a limited, directed electric arc to classify the material and clothing into 2 protection classes prescribed in EN 61482-1-1.
-Arc Intensity Iarc: Actual intensity flowing in the circuit during the duration of the arc expressed in effective kA.
-Warc arc energy: The sum of the instantaneous arc tension multiplied by the instantaneous arc intensity multiplied by the time increments of the arc duration expressed in kJ or kW·s.
-Arc Interval: Distance between the arc electrodes
-Thermal protection against arcing: for garments, the thermal performance of arc is obtained by evaluating the burning time, formation of holes, fusion and operation of fasteners as well as accessories.
-Arc tension: expressed in V.
-Peak delta temperature ΔTp: Difference between the maximum temperature and the initial temperature of the sensor during the exposure time expressed in ºC.
-Incident energy of direct exposure, Ei0: Thermal energy or incident received by a calorimeter which has been emitted by the electric arc expressed in kJ/m2 or kW·s/m2 (cal/cm2).
-Electric arc: Gaseous conduction in which electrons are the majority of the charge carriers produced by primary electronic emission.
-Thermal flow: It is the amount of energy transmitted per unit area and time expressed in kW/m2.
-Incident energy, Ei: Total heat received per unit area as a result of an electric arc expressed in kJ/m2 or kW·s/m2 (cal/cm2).
-Expected short-circuit current: The predicted current that will flow when the arc electrodes are connected by a conductor expressed in kA rms.
-Stoll curve: It is an empirical model for predicting 2nd degree burns of the skin by relating the amount of thermal energy transferred to the humble tissue and the time of exposure.
-Test intensity, Iclass: Intensity of the expected short circuit expressed in kA rms.
-Time to peak delta temperature, tmax: Time expressed in seconds, from the start of arc priming to reach peak delta temperature.
-Transmitted energy, Eit: Incident energy received by a calorimeter when testing clothing or material expressed in kJ/m2 or kW·s/m2 (cal/cm2).
The test plate shall be made of a non-conductive heat-resistant material of 400 x 400 ± 10 mm with a minimum thickness of 10 mm.
The sample to be tested will be 500 mm ± 10 mm long and 500 ± 10 mm wide cut according to the length and width of the material. 4 samples will be analyzed. If one of them does not meet the acceptance criteria, a fifth sample will be tested. No more than 5 samples can be taken.
Samples must be pre-treated by pre-cleaning according to the manufacturer’s instructions or 5 cycles of washing and drying. Then they must be conditioned between 18 – 28 ºC with relative humidity of 45 – 75 % at least 24 h.
The specimens will be folded around the test plate in a flat position. The material will be fixed on the back of the plate ensuring optimal contact with the plate without the presence of air between the sample and the calorimeter.
If the test is for bottoms, a dummy with hips and legs may be used using the center of the electrode range at the crotch.
If other parts of the garments are of interest, it can be tested on a flat test plate.
The circuit must have the ability to give a near-constant source of alternating voltage and short-circuit current. 50 and 60 Hz are allowed for alternating current.
A fuse wire connected to the ends of the opposing electrodes should be used and this will be consumed during the test. This wire will be made of copper with a maximum diameter of 0.5 mm.
Characteristics of the goal:
-Test voltage: 400 V ± 5% alternating current
-Iclasse test intensity: for class 1, 4 kA ± 5 % and for class 2, 7 kA ± 5 %
-Arc duration: 500ms ± 5%
-Frequency: 50 ± 0.1 Hz or 60 ± 0.12 Hz
The sample rate must be at least 5 kHz
Temperature should be sampled at least 5 ms per channel for 30 s at 0.1 °C resolution.
The garment must be made with all its standard inclusions, zippers and pockets. This garment will be pre-treated according to the manufacturer’s instructions based on standardized processes. If no instructions are specified, the test will be carried out after 5 washing and drying cycles.
The sample should be conditioned for at least 24 hours at 18–28 ºC with a relative humidity between 45–75% and tested within 5 minutes after conditioning.
At least 1 garment sample will be tested. Additional samples will be required in case the arc energy during the discharges is out of range.
The test shall be carried out at an ambient temperature between 15 and 35 °C with a relative humidity of 25 to 75 %.
Incident energy Ei: it will be calculated by multiplying the peak delta temperature by the sensor constant 5.52 kJ/m2 ºC. The incident energy of direct exposure Ei0 and the 4 values of the transmitted energy Eit must be determined, as well as the mean value of the 4 Eit values and their 95 % confidence interval
Sensor response to the Stoll curve: the Stoll curve must be superimposed on the trace of the 4 pairs of values (Eit and time to the peak delta tmax) and also on the trace of the 4 heat curves Eit(t) of the incident energy transmitted.
A visual inspection will be performed once the samples are cool.
The test will be considered a PASS when:
-The material of the garment has passed the test for materials
-The pledge complies: the burning time is less than or equal to 5 s; there is no fusion through the inner side; There are no holes larger than 5 mm in the innermost layer. Accessories will not have any negative influence on the results.
