The ambient temperature. If it’s very hot where the body is it might start to smell within 10 - 12 hours. If it’s very cold, like the Arctic, and never gets above freezing it may barely smell at all.
Humidity. If it died in a humid area it will begin to smell fairly quickly, within a day or two. If it died in a hot, dry desert, it might dry out before it started to rot and not smell much at all.
Cause of death. If it died from something like a heart attack, it may not smell for 2 or 3 days. If it died from a traumatic injury, such as an accident that broke open the abdominal cavity then it might start to smell almost immediately. (The open abdomen is a smell you won’t quickly forget)
What was recently ingested. If it died after having recently had a lot of alcohol there will be a very distinctive, sickly sweet smell. If it died after eating something very spicy it might smell strongly of that spice.
https://www.quora.com/Decomposition-How-long-does-it-take-for-a-dead-body-to-start-smelling
150 dead bodies concentrated in a small area would be almost unbearable. Just sayin
Psst, there are two twin towers. The tower that collapsed was the South Tower, and people are the North Tower are staying put.