Answer :
Final answer:
Fire streams directed into ventilation openings reduce the effectiveness of vertical ventilation by disrupting airflow dynamics and potentially pushing heat and smoke back into cleared areas.
Explanation:
The effectiveness of vertical ventilation can be reduced by factors such as personnel working ahead of the fire, which could include trench cuts too small, or fire streams being directed into ventilation openings. However, the factor among the options provided that specifically reduces the effectiveness of vertical ventilation is c. Fire streams directed into ventilation openings. This happens when the water from the fire streams interferes with the intended airflow dynamics, disrupting the chimney effect that vertical ventilation is meant to achieve, and potentially pushing heat and smoke back into previously clear areas.
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