3.3.8 Calculation of damage frequency (failure rate)

In IEC 62305-2, only a single damage risk is now calculated. This includes, in particular, loss of life and physical damage to and within the structure and its contents. This risk of damage is therefore best compared as an overlap of the two types of damage, L1: loss of human life and L3: loss of cultural heritage from the previous edition of IEC 62305-2. This can also be clearly seen from the relevant risk components in Table 3.3.6.1. The risk of damage consists in particular of the risk components R_A, R_B, R_U and R_V, i.e. components that are primarily based on the causes of damage D1D, D1T and D2, i.e. electric shock and fire, explosion, etc. The surge-related components R_C, R_M, R_W and R_Z resulting from cause of damage D3 are only relevant here in ‘exceptional cases’, i.e. where surges have a direct impact on human life (e.g. in hospitals) or cause explosions in correspondingly hazardous facilities. 

The types of damage L2: Loss of service to the public and L4: Economic losses from the 'old' second edition of the standard were mainly due to components relevant to overvoltage, i.e. the service was particularly vulnerable to overvoltage, and economic losses were also a result of such overvoltage. They were therefore a consequence of the failure of electrical and electronic equipment rather than physical damage to the structure. With the 'old' types of damage, however, a loss factor still had to be determined in order to calculate the risk of damage, or a cost-benefit analysis had to be carried out. Neither was ever easy.

In IEC 62305-2, it has therefore been agreed that the risk of damage will no longer be calculated for these damage effects, but rather the frequency of damage (Equation 3.3.8.1). This is also based on the parameters frequency of hazardous events N_X and probability of damage P_X: