Air Management in the Fire Service

Keywords: air management, firefighter physiology, large structures, health and safety

BACKGROUND ON AIR MANAGEMENT

Inside a burning structure, the firefighters’ only line of defense between themselves and the extreme environmental conditions is wearing the personal protective ensemble (PPE), consisting of bunker pants, jacket, flash hood, gloves, boots, and helmet, as well as a self‑contained breathing apparatus (SCBA). The ability to perform efficiently during fire suppression relies on the amount of air contained within the SCBA cylinder. Many fire departments operate on ‘30 minute’ air cylinders with a maximum pressure of 4,500 psi containing approximately 1240 L of air; however, with an absolute quantity of air contained within each cylinder, a firefighter’s physiological characteristics will determine the maximum amount of time he/she will be able to work while breathing through a single SCBA tank.

The primary challenge revolves around the fact that the SCBA was developed for single-dwelling use. Structural fires occurring in high rises, large department stores, or in a subway system pose a significant challenge to firefighters. The origin of the fire may be a sizable distance from the entrance to the fire scene and could result in the firefighters consuming a large proportion of their SCBA cylinder before reaching the fire. The small amount of air that remains would not be sufficient to perform critical firefighting tasks while maintaining adequate air supply to allow for safe evacuation from the fire scene. The ability to manage air supply with respect to controlling the amount of time in the hazardous area is known as ‘air management’. (National Fire Protection Association, 2006).

Currently, the modern SCBA is equipped with a digital heads-up display (HUD) that allows the firefighter to monitor the amount of time remaining on their SCBA cylinder based on the current rate of air consumption. The main problem with this technology is that fire suppression tasks are not steady‑state, with work intensities changing very quickly and dramatically changing rates of air consumption. The second safety device installed in every SCBA is the low‑air alarm, which is programmed to sound an audible alarm when there is 33% of air remaining in the cylinder. In 2013, the National Fire Protection Association (NFPA), amended NFPA 1981 to raise the limit for the low‑air alarm to 33% from the previous standard of 25%. With the standard ‘30 minute’ air cylinder, the 33% low‑air alarm theoretically sounds when there is 9.9 minutes of breathable air supply remaining1. As every firefighter is different in terms of body size, muscular strength, and aerobic conditioning, this reported 9.9 minutes of remaining air supply when the low‑air alarm sounds might be a significant overestimate of the actual time remaining for an individual. This overestimate is due to the varying work intensities required of firefighters with more vigorous job tasks demanding a higher rate of air consumption, therefore, reducing the amount of time a firefighter can breathe while on‑air. The proposed formula for optimal and efficient air management is1:

SCBA Air Volume = Work Period + Exit Time + Margin of Error for Self‑Rescue

Based on this formula and with the current low‑air alarm standard of 33%, firefighters would be required to utilize the other 67% of their air supply during the ‘work period’ and ‘exit time’.

It is critical that efficient strategies be developed to ensure that firefighters and other emergency personnel can safely enter an emergency scene, perform their tasks and safely exit the structure before there is risk of running out of air.

PREVIOUS RESEARCH

In 2007, research was conducted at the University of Waterloo by Dr. Richard Hughson and Dr. Michael Williams‑Bell in collaboration with the Toronto Fire Services. The purpose of the research was to determine the air management required when performing firefighting tasks in large structures (high‑rise buildings, box stores, subway systems)2,3. One scenario was conducted at Toronto City Hall to determine the air requirements for Fifth‑Floor Search and Rescue Scenarios. Here, firefighters had to complete a 5‑flight stair climb, conduct a 3‑room victim search and hose drag, a forcible entry simulation, followed by a 75‑foot victim rescue drag (165 lbs), and a 5‑flight stair descent. This scenario allowed the researchers to determine the physiological demands during critical tasks encountered in high‑rise fires.

THE SPECIFIC TASKS PERFORMED IN THE FIFTH‑FLOOR SEARCH AND RESCUE

The normal maximum number of floors climbed before entering a fire area is five floors. The researchers examined the air consumption for climbing the five floors, searching through three rooms while advancing a hose line, performing a forcible entry, dragging a victim then safely returning to the ground floor and exiting the structure. The data from the previous research study in terms of average completion time, heart rate, breathing volume, and air consumption are shown below. It should be noted that the data from the previous research study allowed full visibility and did not include elevated air temperatures and humidity in the environment.

Figure 1: The table represents the air management data measured during the fifth-floor search and rescue scenario from previous research. The information in the table depicts the amount of air consumed from the SCBA air cylinder (in % of air used from the tank) for climbing 5 floors, performing a search of 3 rooms, dragging 165 lbs victim, and descending 5 floors to achieve a safe exit. In addition, the average time required to complete a forcible entry task as well as the total time to conduct the scenario, time to low‑air alarm (corrected to 33%), and the air consumption (in % of air used from the tank) for the entire scenario and to low‑air alarm are represented. All data is the average from 36 firefighters.

WHAT DOES THIS STUDY TELL US ABOUT AIR MANAGEMENT?

The duration of the search and rescue scenario was relatively brief (from 4:11 to 9:38 mins for the individual firefighters). Therefore, average air consumption was only 37% of the cylinder (ranging from 25 to 51%) and no low‑air alarms were activated at any point during the simulation. However, for these individuals, it was predicted that the low‑air alarm could sound in 9 min. It was extrapolated that 50% of firefighters would have had their low‑air alarm activated if they had continued to work for a total time of 11 min. It is important to recognize that the extrapolations are simply predictions based on a linear model of air consumption. However, it is not known if the firefighters participating in the research study would have been able to sustain the same level of work intensity for the duration of the activity before they ran out of air. It is likely that they would have reduced their work intensity and possibly increased the amount of time they were able to breathe on‑air. However, the data on air consumption taken together with the measured metabolic requirements of the search and rescue can be utilized to consider a frequently asked question in the fire services as to whether firefighters should use a larger cylinder to increase the level of safety. The current data and other recent evidence argue strongly against this practice.

KEY POINTS

• SCBA air cylinders are rated for moderate intensity exercise; many firefighting tasks will cause you to deplete your air cylinder in a much shorter time frame.

• Tasks, such as stair climbing and search and rescue, can result in low‑air alarms sounding in as little as 8 to 12 minutes.

• Elevated air temperatures and increased humidity will result in higher heart rates and breathing rates leading to faster SCBA air cylinder depletion.

HOW DOES WEARING AN SCBA IMPACT MY BREATHING?

The relatively long period involved in advancing a hose and searching while crawling on hands and knees is a typical task in a structure fire. Importantly, the level of ventilation (the volume of air that you are able to breathe in a minute) sustained during this crawling activity was very high ranging from 63 – 131 l/min while the firefighters were in the second room. Although the maximal exercise capability was not measured in these individuals while wearing the SCBA, findings showed limitations in expired ventilation (VE) and oxygen consumption (VO2) while wearing the SCBA. It was reported that a 17.3% reduction in maximal oxygen consumption (VO2max) from 52.4 to 43.0 ml/kg/min due in part to a 14.5% reduction in peak ventilation from 167 to 143 l/min while breathing from the SCBA4. There are major implications for the work of breathing and possible breathing limitations during the previous study especially considering the crawling position in which the arms and back were used to support movement. It might be anticipated that this could further restrict ventilation while wearing the SCBA.

ARE LARGER AIR CYLINDERS THE ANSWER TO IMPROVE SAFETY?

Data from previous studies reflecting the extremely strenuous nature of firefighting suggest that any attempt to have firefighters work longer by supplying larger cylinders for the SCBA would simply result in greater levels of fatigue from which it would be extremely difficult to recover. It is well known that the maximum total high-intensity work is accomplished by short periods of activity with rest intervals5. Therefore, under conditions where firefighters perform active duty cycles at a fire scene, it is best to keep the work period relatively short for two key reasons. First, longer cycles will cause greater fatigue with increased likelihood of injury. Second, as we have demonstrated, individual firefighters can consume air at such a rate that their low‑air alarms are activated in less than 10‑min. Firefighters should be safely out of emergency fire situations before their low‑air alarm sounds allowing for unexpected emergencies including the possible need for self‑rescue1.

REFERENCES

1. Bernzweig, D., EXPANDING “TIME TO EXIT” FOR FIREFIGHTERS Exit time, or escape time, is a serious issue facing the fire service. How you can lobby for better protection. Fire Engineering, 2004. 157(6): p. 63–68.

2. Williams Bell, F.M., et al., Air management and physiological responses during simulated firefighting tasks in a high rise structure. Appl Ergon, 2010. 41(2): p. 251–9.

3. Williams Bell, F.M., et al., Physiological responses and air consumption during simulated firefighting tasks in a subway system. Applied Physiology, Nutrition, and Metabolism, 2010. 35(5): p. 671–678.

4. Dreger, R.W., R.L. Jones, and S.R. Petersen, Effects of the self‑contained breathing apparatus and fire protective clothing on maximal oxygen uptake. Ergonomics, 2006. 49(10): p. 911–920.

5. ASTRAND, P. and K. RODAHL, Textbook of work physiology: physiological bases of exercise (86). 1986.