This part of the UNE 53-558 standard specifies a method to evaluate the resistance to cracking of vulcanized rubbers or thermoplastics subjected to dynamic traction while they remain exposed to air with a certain concentration of ozone and at a defined temperature, in circumstances in which They exclude the effects of direct light. When relating the standardized results to the behavior in service, one must be very cautious, since the relative resistance to ozone attack of the different rubbers can vary depending on the test conditions and, in particular, the concentration of ozone and of the temperature. Furthermore, the tests are carried out with thin specimens deformed in tension, and the meaning of the attack for articles in service can be very different, due to the effects of their size and the type of deformation. Explanatory notes on the nature of ozone cracking are given in the annex. In the first part of the UNE 53-558 standard, methods are indicated to determine the resistance to ozone cracking in specimens subjected to static traction. The third part of the UNE 53-558 standard will be dedicated to the presentation of a method for evaluating ozone concentration.