Random Section of **GOST 12.1.004–91**

3.1.14. Probability (*Q _{i} *(

*e*

_{3})) during continuous work of electric appliances shall be unity for all facilities if electric equipment does not correspond to the combustible medium category and group or 10

^{-8}if it corresponds to the appropriate category and group. In case of periodic operation of electric equipment and its failure to correspond to the combustible medium category and group, probability (

*Q*(

_{i}*e*

_{3})) shall be calculated analogous to probability (

*Q*(

_{i}*a*)) in accordance with (42). If electric spark is formed only at start / stop of electric equipment that does not correspond to the combustible medium category and group in the case of

_{n}*n*starts / stops, probability (

*Q*(

_{i}*e*

_{3})) shall be calculated analogous to probability (

*Q*(

_{i}*t*

_{2})) in accordance with (49). If electric equipment is in compliance with combustible medium, probability (

*Q*(

_{i}*e*

_{3})) calculated from (49) shall be multiplied by 10

^{-8}.

3.1.15. Probability (*Q _{i} *(

*e*

_{4})) of the static electricity spark formation in the

*i*th facility element shall be calculated as

(*Q _{i}
*(

*e*

_{4}) = (

*Q*(

_{i}*X*

_{1}) · (

*Q*(

_{i}*X*

_{2}), (57)

where *Q _{i}
*(

*X*

_{1}) is the probability of gaining static electricity in the

*i*th facility element during a year;

*Q _{i}
*(

*X*

_{2}) is the probability of failure, absence, or inefficiency of protection from static electricity during a year;

3.1.16. Probability (*Q _{i} *(

*X*

_{1})) shall be assumed equal to unity if substances with specific volume electric resistance exceeding 10

^{5}Ohm·m are used in the

*i*th facility element. In other cases, (

*Q*(

_{i}*X*

_{1})) is assumed to be zero.

3.1.17. Probability (*Q _{i} *(

*X*

_{2})) shall be assumed equal to unity in the case of absence or inefficiency of static electricity protections. Probability (

*Q*(

_{i}*X*

_{2})) of protection means failure in operating elements shall be calculated based on of statistical data analogously to probability (

*Q*(

_{i}*a*)) in accordance with (42).

_{n}Probability (*Q _{i} *(

*X*

_{2})) in the designed facility elements shall be calculated analogously to probability (

*Q*(

_{i}*a*)) in accordance with (43) based on the data on reliability of design means of protection from static electricity (for example, ionization, air dampening, etc.).

_{n}3.1.18. Frictional sparks (shock and friction
sparks) result in the facility element under study (event *HS _{n}*) from using intrinsically unsafe tools (event

*f*

_{1}), destruction of moving units and components (event

*f*

_{2}), using footwear with metal elements and nails (event

*f*

_{3}), ingress of foreign items into moving mechanisms (event

*f*

_{4}), etc., metal hatch impact (event

*f*

_{5}). Probability (

*Q*)) shall be calculated as

_{i}(HS_{n}*Q _{i} (HS_{n}*) = 1 — [1 —

*Q*)], (58)

_{i}(f_{n}where

*Q _{i}
*(

*f*) is the probability of realization of any of

_{n}*f*causes shown below;

_{n}*Q _{i}
*(

*f*

_{1}) is the probability of metal, grinding, or other intrinsically unsafe tool use in the

*i*th facility element during a year;