Change for the Better? – Part 4
Written by John on November 20th, 2009
THE CHANGING FIREGROUND ENVIRONMENT
Additionally, two additional concerns related to the fireground environment should be carefully evaluated:
- Has the fireground environment decreased your endurance and ability to make sound decisions? It is a fact that when the human body is fully encapsulated by protective equipment and is subjected to a hot-working environment, the body will try to ventilate itself by sweating. As there is minimal air flow over the skin, the body will continue to sweat to provide some degree of relief from rising body temperatures. Unfortunately, this results in “sweat-wetting” which reduces the fluid level in the human body, and decreases the level of human endurance (strength) and the ability to make sound decisions. Therefore, when personnel are subjected to a hot-working environment, they should consider devoting time to rest and rehydrating lost fluids. A common rule is: “when two bottles are used in the environment, at least 10 minutes rest with appropriate fluid intake should be considered before additional work is allowed.”
- If the modern thermal layer and potential of flashover has increased in frequency and degree of hazard, what form of ventilation has the potential to most effectively reduce the danger of these two considerations? This question is best answered by briefly considering horizontal, vertical, and pressurized ventilation. Although horizontal ventilation is the most popular due to its ease and safety of implementation, it does not take advantage of the natural path of travel (vertical or upward) of heated gases and smoke. It also has a minimal effect on the hottest portion of a room (ceiling), which is where most flashovers originate. Therefore, horizontal ventilation will ventilate that portion around the opening (open door or window) but have the potential to have minimal effect on minimizing a flashover. Vertical ventilation will take advantage of the natural path of travel of heated contaminants (upward) and ventilate that portion of a heated environment that needs it the most (ceiling area). However, vertical ventilation takes additional time, staffing, and equipment to be accomplished. Pressurized ventilation (i.e., positive pressure ventilation) can enhance horizontal and vertical ventilation operations, but must be used judiciously used when fireground operations favor its implementation. In summary, chose your method of ventilation carefully, and do not rely on opening windows and/or doors to ventilate the contaminated area and improve the thermal layer to minimize the potential of flashover, as you may be tragically disappointed.
Finally, let’s discuss one last issue regarding fire attack operations in today’s fireground environment. Approximately 30 years ago, new firefighters were instructed to not use a nozzle until they could see fire and/or the seat of a fire. An additional note of wisdom went something like this: “You can always recognize a good engine company by the lack of water on the floor.” These two concepts emphasized that water was not to be used until you could actually see fire, and, excess water in a structure had been inefficiently used and would need to be cleaned up. Recently, a growing number of fire instructors are teaching two new concepts that share a strong commonalty of using water to control the environment as follows:
- Penciling: This concept has primarily evolved from the Swedish Flashover Training Simulator that allows students to visually experience a growing fire and resultant thermal layer at the ceiling. If the fire is allowed to grow, students are soon forced to the floor by the increasing heat at the ceiling, and, some flames at the ceiling will soon follow. This indicates the thermal layer (fire gases) is reaching its ignition temperature (or, are approaching a flashover). Students are instructed to direct short, thin streams from a nozzle at the ceiling. If accomplished correctly, the concept of penciling will graphically reduce the temperatures at the ceiling, minimize the potential of flashover, and not destroy the thermal layer at the ceiling.
- Thermal Layer: An interesting program (FIRE!) recently aired on the Discovery Channel and focused on studies conducted by Sweden and England. Interestingly, the program explores the feasibility of fire gases and smoke being more dangerous than the actual fire itself. The program displayed excellent examples of using the concept of penciling to reduce the threat of the thermal layer to advancing suppression personnel, and in some cases, actually knocking a fire down by using expanding steam in a confined environment without personnel being in the environment (similar to indirect firefighting of 30 years ago?).
Therefore, if fire gases and smoke encountered by the firefighters of today (and tomorrow) have the potential to more easily flashover as compared to the environments of yesterday, then, is it possible that smoke and fire gases encountered before reaching the seat of a fire might be a higher priority to personnel safety than the fire itself? Interesting food for thought!
