2.1.1. The triangle - collapsible triangles are to be assembled as for use - shall be immersed for 10 minutes in water having a temperature of 50 °C ± 5 °C, with the highest point of the upper part of the illuminating surface being about 20 mm below the water surface. Immediately afterwards, this retro-reflective device shall be immersed under the same conditions in water having a temperature of 25 °C ± 5 °C. a0c0