Smoke Generators

 


  "We don't fight as many fires as we used to and that makes it difficult for our newer firefighters to learn through experience." This statement echoes through many firehouses and often goes along with discussions on the increased importance of good training to provide firefighters with the...


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After a continuous-operation smoke generator was activated in each wing, responders were called in for a structure fire response. Crews were not briefed on the exact scenario they would be faced with, but were instead challenged to properly size-up the incident and take action. The fire department crews were divided into search-and-rescue and fire suppression teams. Closely monitored by instructors, the search team entered the building with thermal imaging cameras. Due to the density of the smoke, the firefighters had to hold the thermal imaging cameras directly to their facepieces in order to see the screens. The fire suppression team experienced similar difficulties advancing dry hose through the building.

Rescues of training manikin "victims" were quickly made and the seat of the fire was discovered, but the large area and dense smoke proved to be a challenge for crews and the time required to conduct these operations was longer than expected. A few firefighters became disoriented and separated from the team during the exercise.

In addition to the experience gained by the firefighters in large-area search, thermal imaging techniques and long hoseline stretches, they were able to test their own ability to respond to a high-occupancy building in their district. By reviewing the lessons learned in the critique, the participants gained insight that will help if ever faced with an emergency at this or a similar location. Instructors were also able to gauge the strengths and weaknesses of the response, which will be used to shape future training programs.

Although most drills conducted with smoke generators are based around structural firefighting tactics, training does not need to be restricted to indoor usage. Brought outdoors, smoke generators can also set the scene for hazmat incidents, motor vehicle accidents and CBRNE (chemical, biological, radiological, nuclear and explosives) training exercises.

All water-based smoke machines operate under the same basic concept: smoke liquid, which is primarily a mixture of deionized water and various glycol-based compounds, is pumped through a heater, vaporized into smoke and forced out of the machine. However, there are a number of factors that determine the properties and quality of the smoke. A major variable is the temperature at which the smoke is vaporized. When the heater temperature is maintained at the optimal temperature for the smoke liquid used, the resulting smoke has a more uniform particle size and temperature. The more uniform the particle size, the denser the smoke; the more uniform the temperature, the longer the hang-time of the smoke. In simpler terms, precisely controlling the temperature results in a more uniform, heavier, denser smoke that is generally more like structure fire smoke than "fog."

If smoke is produced below the optimal temperature, the smoke liquid may not be fully vaporized, resulting in "wet" smoke that is more likely to leave a residue. Smoke produced above the optimal temperature results in burnt particles, which reduces the density of the smoke and reduces the efficiency of the machine by using more smoke liquid to achieve the same low-visibility conditions.

In more basic smoke machines, as the heat energy is transferred from the heaters to the smoke liquid, the heaters inevitably cool down. Once below a certain temperature smoke can no longer be generated, which is why these machines need time to reheat and recharge between discharges. To measure heater temperature, these machines use two thermostats: one to signal when the heater has reached its high-temperature setting and the other to signal when the heaters have reached the low-temperature setting and need to reheat. When the low-temperature setting is reached, smoke production is stopped until the heaters recover and trigger the high-temperature thermostat.

More advanced smoke generators can continuously produce smoke by replacing the two-thermostat system with a temperature-control system that balances smoke liquid delivery with heater temperature. By continuously monitoring temperature, these smoke generators can increase or decrease the amount of liquid pumped to the heater so optimal smoke vaporization is achieved. If the heater temperature measures slightly above the optimal temperature, the smoke generator can increase the liquid delivered to the heaters or reduce the power supplied to the heaters. If the heater temperature begins to dip, the power supplied to the heaters is increased and/or the liquid pumped to the heaters is reduced. The result is a balance of heat capacity and liquid delivery that continuously produces smoke. Further, the smoke is produced at a more specific, consistent temperature, which improves uniformity of particle size and smoke temperature, instead of throughout a range of temperatures.