# Material Composition Testing Related to Measurement Instrument Enclosure Design and Safety
## 2 Testing Method  
Testing Procedure for 50 W Horizontal Flame Test (method A) provides valuable data for comparing the relative burning behaviour of various insulating materials, controlling manufacturing processes, or assessing changes in burning characteristics. The horizontal orientation of the test specimen is specifically suited to evaluating both the extent of burning and the flame propagation velocity (linear burning rate). The equipment used for performing the test included:  
* Laboratory fume hood/chamber: Volume of 0.5 m\({}^{3}\), with dark walls and recorded light levels below 20 lx, equipped with an exhaust fan (switched off during the test) and a positive closing damper. * Laboratory burner compliant with IEC 60695-11-4 standard. * Specim holder with clamps to securely position the test specimen. * Timing device with a resolution of at least 0.5 s.
* Measuring scale graduated in millimeters. * Wire gauze (20 mesh), compliant with standards. * Conditioning chamber-maintaining conditions of 23 \(\pm\) 2 \({}^{\circ}\)C and 50 \(\pm\) 5% relative humidity (RH). The bar-shaped test specimens measured 125 \(\pm\) 5 mm in length and 13.0 \(\pm\) 0.5 mm in width, with a maximum thickness not exceeding 13 mm. The edges of the specimens were smooth, with corner radii not exceeding 1.3 mm. Alternative thicknesses were permitted by mutual agreement between relevant parties. A maximum of six specimens per material combination were prepared for testing. Figure 1 illustrates the positioning of a test specimen on the test stand, showing the wire gauze beneath the specimen and the burner in its required position. Before testing, specimens were conditioned for 48 h in a controlled environment at 23 \(\pm\) 2 \({}^{\circ}\)C and 50 \(\pm\) 5% RH. Figure 2 presents the conditioning setup for the test specimens. Figure 3 demonstrates the actual test apparatus setup during testing. We fixed each bar-shaped specimen horizontally on the stand, with the transverse axis inclined at an angle of 45 \(\pm\) 2\({}^{\circ}\). The wire gauze was positioned horizontally 10 \(\pm\) 1 mm below the specimen's lower edge. For method A (horizontal burning), testing was conducted in laboratory conditions with ambient temperatures ranging from 15 \({}^{\circ}\)C to 35 \({}^{\circ}\)C and a relative humidity ranging from 45% to 75%. Each specimen was marked with two perpendicular lines relative to its longitudinal axis, located 25 \(\pm\) 1 mm and 100 \(\pm\) 1 mm from the ignition end. We applied the flame from the burner on the edge of the sample (as presented in Figure 1) steadily for 30 \(\pm\) 1 s or removed it immediately once the flame front reached the 25 mm mark. The timing device was reset when the flame front reached the 25 mm mark. If the specimen continued to burn after flame removal, we recorded the burning duration from the 25 mm mark until it passed the 100 mm mark. If the flame front exceeded 25 mm but did not reach the flame front, the flame front exceeded 25 mm. Figure 1: Test specimen positioned on the test stand. Figure 3: Actual setup of the test apparatus during flame testing. Figure 2: Conditioning of test specimens in the climatic chamber. 100 mm, both the elapsed time and damaged length were recorded. If any specimen from the initial set of three failed to meet the classification criteria, a second set of three specimens was tested. All specimens from the second set had to meet the required criteria. The linear burning rate (\(v\), in mm/min) for specimens whose flame front passed the 100 mm mark was calculated using the following:  
\[v=(60\times l)/t \tag{1}\]  
where \(v\) = linear burning rate (mm/min), \(l\) = damaged length (mm) and \(t\) = time (s). Materials Classification Criteria  
We classified materials according to EN 60695-11-10 into HB, HB40, or HB75 categories, based on the following criteria:  
* HB classification: (a) The material does not visibly burn after the removal of the ignition source. (b) If burning continues, the flame front does not pass the 100 mm mark.