"This was really thick, nasty, black brown smoke with high heat," Chief Mike Tobin of Lansing Emergency Management said.
It decreased a firefighter's visibility, while increasing the temperature of the building.
"This is all that smoke buildup as its been traveling," he explained. "Down around here is probably about where the base of the smoke would be in this hall."
A hall in the old Walter French School that's located about 300 feet from where the fire started.
"That area of the building is not just inside of a door, they had to go in the door, on air, traverse anywhere between 150 and 200 feet, just to get to that portion, dragging all of their hose lines, everything with them and then fight the fire on top of that," Chief Tobin said.
The pool room was the primary fire room. It's got a pool with a floor built over it and no windows. So, Chief Tobin told us throughout the five hour operation, temperatures reached between 600 to 1100 degrees.
"Plus roughly 125 pounds worth of gear - equipment and hose, put that in extremely high temperature conditions and then outside we had high humidity conditions. It was later in the day. It can really zap someone, very quickly," the Chief added.
And it did. Five of the eighty-five firefighters were treated at the hospital for heat exhaustion.
Chief Tobin told News Ten that's hard to prevent, but they do plan for the hot conditions.
"We'll adjust the daily schedule - along the lines of we may reduce the training activities, change training activities," he said. "The guys on those days will change their meals, they'll eat lighter meals."
And, on scene resources will increase faster and come in larger numbers. CATA brings in air conditioned buses and a paramedic sets up a rehab area to change each responder's oxygen and check their vitals.
"We're constantly rotating 'em in, so they're getting about a 20 to 30 minute break as the evolution goes on," Chief Tobin explained.
Working to stay cool before running back into the heat.
An Emergency Room doctor at McLaren Hospital tells News Ten you don't have to experience conditions that extreme to get heat exhaustion or dehydrated.
Dr. David Komasara said if you're outside, stay in the shade and drink double the amount of water you'd normally drink.
The ER at McLaren has seen about 20 patients in the past three days with heat-related illnesses.