Final answer:
In tunnels and underground areas, it is generally recommended to allow at least 30 minutes for smoke to leave the blasted area, depending on various factors.
Step-by-step explanation:
In tunnels and underground areas, the time required for smoke to leave the blasted area depends on various factors, such as the size of the tunnel, ventilation systems in place, and the amount of smoke produced. However, a commonly used estimate is to allow at least 30 minutes for smoke to dissipate.
During this time, the smoke can be cleared through proper ventilation systems or natural air flow, ensuring the air quality is safe for people to enter or for emergency personnel to conduct rescue operations.
It's important to note that smoke inhalation can be extremely dangerous and even deadly, so it's crucial to follow safety protocols and evacuate the area until it is deemed safe to re-enter.