How many meters of water wells in hot work area can prevent sparks from falling and causing explosion?

/kloc-within 0/5 meters. Shielding measures should be taken for hot work at heights to prevent sparks from splashing. Water wells and floor drains within the hot work area 15m must be sealed to prevent sparks from falling and causing explosion. Sewer shaft is a kind of urban public facilities, which refers to the pipeline for discharging sewage and rainwater from buildings, and also refers to the underground passage for discharging sewage, domestic wastewater and rainwater in cities, factories or villages.