Have you ever noticed a hose, that you recently installed, start to crack and separate at the seams? This is generally caused by Ozone/Ultra Violet light affecting the outer cover of the hose and can happen rather quickly to new hose or take more time over several years. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth’s atmosphere.
EI 1529 states in Section 4.4.12, Ozone Resistance:
The cover material shall not show signs of cracking when subjected to the ozone test.
Section 6.5.11, Ozone Resistance Test:
The cover material is tested for signs of cracking in accordance with ASTM D 1149 or ISO 7326, using test conditions of 100 parts of ozone per hundred million parts of air by volume for a 72-hour period at a temperature of 40 °C ± 1 °C (104 °F ± 2 °F).