Grading the Fireground On a "Curve"

Mark Emery discusses the dangers on the fireground and the need to observe fire growth accurately.


A Benign-Looking Fireground Can Be a Deadly Fireground Two National Institute for Occupational Safety and Health (NIOSH) fatality investigation reports, 98-FO7 and F2004-14, involve firefighters advancing into obscured-visibility, low-heat conditions. In both cases, as they began their advance...


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On the fire-growth side of the curve, value diminishes as the curve ascends; on the decay side, there is no value. Anybody or anything that is unprotected on the decay side is history. On the growth side, value diminishes as minutes pass and temperature rises toward flashover. After flashover, the fire will free-burn until it depletes available oxygen or it runs out of stuff to burn. Horizontal ventilation on the decay side of the curve, usually the result of a random act of (fast attack) tactical violence, is like lighting a fuse. As firefighters advance, the fuse smolders. Once the proper fuel/air mixture is achieved, fire growth is resuscitated and the curve turns upward again.

However, as shown by the NIST data, even as the building falls apart, temperatures three feet above the floor don't change much. As shown by NIOSH fatality investigation reports, it is not unusual for experienced, competent fire officers to be seduced by the combination of low heat, limited visibility and the illusion of value. Recall from the NIST photos that the warehouse conditions are not intimidating on the decay side of the curve (until after being horizontally vented). Your thermal imaging camera will tell you what the temperature is, but it won't tell you which side of the curve you are on. Recall that there is a point on each side of the fire-growth curve where the temperature is the same. On the value side of the curve, there can be low temperature and decent visibility; on the no-value side, low heat will be accompanied by obscured visibility.

Remember how a wood-burning stove works: Ideal burn conditions within the stove feature vertical ventilation (an open flue), horizontal ventilation (an open damper), and heat and fuel between the two. Even with the flue wide open, if the damper is closed, the fire will not grow. Review the carbon monoxide data in the NIST report. You will discover that if heat hasn't killed unprotected occupants on the growth side of the curve, carbon monoxide will kill them on the decay side.

My thanks to the Building and Fire Research Laboratory (BERL) and the National Institute of Standards and Technology (NIST) for providing the photos for this article. I would also like to thank NIST and the Phoenix Fire Department for conducting the test that led to the conclusions posited by this article.

VALUE SIDE OF THE FIRE-GROWTH CURVE NO-VALUE SIDE OF THE FIRE-GROWTH CURVE
You can see through the windows You can't see through the windows
Water vapor on inside surface of windows Inside surface of windows look "fuzzy"
Paper signs are still affixed to inside surface of windows Anything stuck to inside surface a window has burned away or shows evidence of heat
Curtains, vertical blinds, etc. are still there Window coverings have burned away or heat damage is evident
Exterior doors are cool to the touch Exterior doors are warm/hot to the touch
(At top of door) (At top of door)
Thermal image camera shows no residual heat on doors and walls (especially metal doors and walls) Thermal image camera reveals residual heat on doors and walls (especially metal doors and walls)
No evidence of smoke stain around upper portion of rollup doors and around any exterior void/penetration where smoke could exhaust under pressure Discoloration caused by smoke around upper portion of rollup doors and around any exterior void/penetration where smoke could exhaust under pressure (see wall discoloration in 5-minute photo)
The fire is reported by someone inside the occupancy Thermal column was reported from across town; you don't see a thermal column while responding
Occupant greets you on arrival and says "the building has been evacuated" Witness claims that "there was lots of fire when I called 911 a few minutes ago"
When in doubt, assume you are on the no-value side until investigation proves otherwise If a fire has been smoldering for a long time you should see oily residue (creosote) buildup on the inside surface of windows
15 FEET FROM THE FRONT DOOR, 3 FEET ABOVE THE FLOOR
3 min. 4 min. 5 min. 6 min. 7 min. 8 min. 9 min. 10 min. 11 min. 12 min.
351F 892F 457F 320F 277F 243F 230F 214F 208F 199F
Top of Curve FFs Enter Door FFs Advance
44 FEET FROM THE FRONT DOOR, 3 FEET ABOVE THE FLOOR
3 min. 4 min. 5 min. 6 min. 7 min. 8 min. 9 min. 10 min. 11 min. 12 min.
469F 1,312F 543F 345F 295F 262F 239F 219F 230F 303F
Top of Curve FFs Enter Door FFs Advance FFs Advance
75 FEET FROM THE FRONT DOOR, 3 FEET ABOVE THE FLOOR
3 min. 4 min. 5 min. 6 min. 7 min. 8 min. 9 min. 10 min. 11 min. 12 min.
204F 602F 431F 324F 279F 257F 225F 217F 466F 565F
Top of Curve FFs Enter Door FFs Advance FFs Advance FFs Advance FFs Retreat