AIR MANAGEMENT: KNOW YOUR AIR-CONSUMPTION RATE

BY DOMINICK MARINO

The engine company officer pauses in the kitchen at the basement door, feeling the doorknob for heat. Dark, acrid-smelling smoke pushes from the top edge of its frame. Turning to the nozzleman, the officer tells the firefighter to bleed the line and mask up. The backup probationary firefighter also places his mask on and pulls his hood into place. As the attack crew stays low and to the side, the officer pulls the door open. One firefighter chocks the door, and they advance down the wooden steps. Visibility is almost nonexistent as the team feels its way down the stairs. Crouching down at floor level, the officer pauses and scans the upper ceiling area with the thermal imaging camera (TIC) for signs of rollover. Seeing none, he drops the camera lower and searches for the fire and any victims in the area. He then pulls back his glove from his wrist and raises it, feeling for heat. He feels moderate heat. He then nudges the team forward, scanning with the TIC as they move. Looking down at his SCBA gauge, he notes that the needle is sitting between 1,500 psi and full. As they crawl across the concrete floor, their progress is impeded by bicycles and small pieces of furniture, which they push aside as they search for the fire. The officer can now see the fire through the TIC off to his left. Reaching for his collar mike, he radios the truck company: “Truck One, take the basement windows side C.”

The truck company acknowledges the order; the sound of crashing glass is heard. He taps the nozzleman, who can now see the glow of the fire, on the shoulder. The nozzleman opens up with a solid stream at the ceiling level. He then drops the stream down onto the main body of the fire. The fire begins to darken down. Suddenly, the low-air alarm of the probie backup firefighter goes off. Forced to abandon the attack, the firefighters start to crawl back out. The officer can hear the probationary firefighter breathing faster as he follows the line back through the cellar. The probie stops suddenly, as his unfastened SCBA’s waist strap becomes entangled with a bicycle. “Control your breathing,” the officer yells to the firefighter, who is struggling to get free. The officer tries to feel where the firefighter is entangled, but because of the low visibility and his bulky gloves, he is unable to determine the point at which the firefighter is snagged. As he radios the rapid intervention team for assistance, the officer wonders if his firefighter will have enough air to make it out.

THE FIREFIGHTER AND THE IDLH ENVIRONMENT

Every day firefighters submerge themselves into atmospheres that are not tenable to human life, and every year some of them do not come back. The factors that lead up to this dilemma can include disorientation, entanglement, overexertion, and overextending our operating time. When we enter into the immediately dangerous to life and health (IDLH) atmosphere, we carry a finite amount of air on our backs. Unfortunately, many times we do not manage this valuable resource wisely. Firefighter fatalities have occurred in the past from running out of air; such events may increase as we push farther into structures because of better turnout protection and thermal imaging cameras that enable us to move faster.

How many of your firefighters have found themselves in a low-air situation? Ask around at your next drill or company meeting. The answer may surprise you.

To many firefighters, air management consists of waiting for the low-air vibration alert or alarm to sound. This occurs when three-fourths of the air supply have been consumed. This procedure during a routine room-and-contents fire in a small building will usually suffice. However, if your egress route is not accessible or an unexpected event occurs, this may not prove to be the case. Another problem is that many times we will employ this same form of nonair management in fire suppression and search operations that are not routine-for example, fires in high-rises, supermarkets, warehouses, and other large areas.


(2). Anticipate the unexpected.

Looking at this form of air management objectively, there appears to be one large shortcoming: You used roughly three-fourths of your air to get to the situation you are currently in. You now have one-fourth of your air supply left to get you out to a tenable safe atmosphere. Remember, air consumption rates depend on several factors that include fitness level, experience, workload being performed, and how efficiently your body metabolizes oxygen. Some of these factors you can change; others you cannot. For these reasons, no two firefighters consume air at exactly the same rate. That low-air alarm is not a signal for the firefighter to leave: It is telling the firefighter that he is running out of air.

Obviously, waiting for the alarm to sound is not an effective way to manage your air supply. However, often in firefighting operations, monitoring your air supply becomes an afterthought until the low-air alert sounds.

THE 30-MINUTE CYLINDER: A POTENTIALLY DANGEROUS MISCONCEPTION

SCBA cylinders are rated in operating pressures and capacity. They are also marked in minutes. As an example, a 2,216-psi, 30-minute carbon-wrap cylinder holds 45 cubic feet of air (1,270 liters) when the pressure gauge reads 2,216 psi. All cylinders will hold their rated volume of air when filled to their rated pressure. The area of concern here is the 30-minute label. Firefighters have to realize that this number is not derived from firefighting activities. The National Institute for Occupational Safety and Health (NIOSH) arrives at this number by placing the SCBA on a machine that simulates an average adult male’s breathing rate at a moderate workload. This rate is based on a respiration rate of 24 breaths per minute with a volume of 40 liters per minute (lpm) (1.41 cu. ft.).

You can verify this by dividing the 40-lpm (1.41 cu. ft.) number into the liter or cubic-foot capacity of the cylinder. Firefighters in the course of their firefighting duties will often exceed these moderate workload factors. National Fire Protection Association (NFPA) 1852, Standard on Selection, Care, and Maintenance of Open Circuit SCBA, states that SCBA regulators will be capable of providing air volumes of up to 103 lpm (3.64 cu. ft.).

In the following example, we will look at the duration of a 2,216 psi-cylinder with the 40-lpm volume (NIOSH testing figure) and then with a 60-lpm (2.12 cu. ft.) volume-the latter’s being more indicative of a firefighter’s workload.

Example:

The 2,216-psi, 30-minute cylinder holds 1,270 liters (45 cubic feet) of air.

-Dividing by 40 lpm (1.41 cu. ft.) (NIOSH) = 31 minutes of usable air.

-Dividing the 1,270-liter cylinder (45 cu. ft.) by 60 lpm (2.12 cu. ft.) = 21 minutes before the cylinder is empty.

If you think this is unrealistic, time your members executing an SCBA confidence course that requires them to navigate through tight quarters while crawling on their knees and stomach. The course we use is a copy of the Pittsburgh Drill run at Fire Engineering’s FDIC. In this drill, two firefighters wearing blacked-out masks work their way through obstacles and snag points. They then perform a reduced-profile maneuver between two wall studs to locate a dummy. The dummy is then extricated along the same course in reverse. The average time to deplete a 30-minute, 4,500-psi SCBA is between 12 and 16 minutes. The least amount of time to deplete the 30-minute cylinder was six minutes; the best consumption time was 21 minutes. These times are taken while negotiating a physically demanding obstacle course that is free of the life-and-death stress associated with being in an IDLH environment.


(1) A firefighter encounters a snag point during the Pittsburgh drill.
(Photos by author.)

null

A SAFER APPROACH TO AIR MANAGEMENT

A technique from the technical diving community can possibly teach us better management of our air.1 Technical diving differs greatly from recreational diving, and so does its air-management strategy. One element common to firefighting and technical diving is that they both take place in hostile environments that often do not provide a direct exit to a safe area. For the diver, this may include operating under ice, inside wrecks, and in underwater caves. Problems the diver may encounter in both environments are disorientation, entanglement, collapses, and task loading. The technical diver, like the firefighter, has a limited air resource.

Technical divers must master the critical skill of air management. In this arena, any time a direct ascent to the surface is not possible, certain air-management principles are implemented. These divers are taught how to compute their individual air-consumption rates so that they can plan their dive and know how many minutes their air supply will last at any given point during the dive. This number is unique to each diver.

A REALISTIC AIR-CONSUMPTION FORMULA

We will examine the air-consumption formula used in the technical diving community to see how it can help us better manage our own air supply. First, however, we must ascertain the air consumption rate (ACR) for each firefighter. This number tells us how much air an individual firefighter consumes per minute while on SCBA. It is a baseline on which to gauge your air supply in minutes when operating. This number will vary during your fire service career according to age, fitness level, the rate of oxygen consumption during exercise (VO2), stress level, and experience, to name a few factors. ACRs will also vary with cylinder size and the cylinder’s rated working pressure. If your department uses cylinders of different sizes (cubic foot volume capacities), you will have to determine specific air-consumption rates for each size cylinder.

Determining a Firefighter’s ACR

To arrive at the ACR, have two firefighters perform an evolution, and record the time spent doing the task and the starting and finishing pressure of the cylinder. Make sure that the cylinders are the same pressure and capacity and are fully charged. For this example, the firefighters are using 30-minute, 2,216-psi cylinders. When this cylinder is full, it holds 1,270 liters (45 cu. ft.) of air.

For our sample evolution, the two firefighters advance a charged handline into a building and up the stairs to a second-floor room. Once there, the firefighters will conduct a basic search pattern. A charged line is used to increase the weight of the hoseline. The weight will make the evolution physically more demanding and will give a realistic consumption rate. You can use your imagination for the type of exercise.

Recording the results of several different types of evolutions will give you an average air-consumption rate for the firefighters. It is important that the firefighters keep moving when performing the exercise. This way, the air-consumption rate will be more representative of an evolution occurring on the actual fireground. If you elect to run your exercises using blacked-out face pieces, have another firefighter monitor the pressure gauges. Remind the firefighters not to use any methods to conserve air such as skip breathing.

Note that most modern SCBA pressure gauges read in psi. Some SCBA manufacturers are now using digital gauges that display psi digitally. These digital gauges enable a firefighter to more accurately monitor their air usage as compared with the analog type.

For this hypothetical example, the firefighters spent 10 minutes completing the evolution. The finishing pressures are recorded on their SCBA gauges. In this case, Firefighter A has a pressure reading of 1,100 psi; Firefighter B, 1,300 psi. Below are the formulas for the two firefighters.

Firefighter A: 2,200 psi (starting pressure) minus 1,100 psi equals 1,100 psi left in cylinder (1,100 psi used).

1,100 psi divided by 10 minutes equals 110 psi per minute ACR;

2,200 psi (rated fill pressure) divided by 110 psi ACR equals 20- minute cylinder duration.

Firefighter B: 2,200 psi starting pressure minus 1,300 psi consumed equal 900 psi used.

900 psi divided by 10 minutes equals 90 psi per minute ACR;

2,200 psi (rated fill pressure) divided by 90 psi ACR equals 24-minute cylinder duration.

AIR-CONSUMPTION RATES FOR 45-MINUTE CYLINDERS

Another firefighter uses a 45-minute, 4,500-psi SCBA (1,840 liter, 66 cu. ft.) and runs the same evolution.

This firefighter’s pressure gauge reached the 3,000-psi mark in 11 minutes. Consumption for this firefighter is 1,500 psi. Dividing the 1,500 psi by 11 minutes equals 136 psi per minute ACR. We can round the 136 psi to 140 psi ACR. This will make the number easier to work with and add a little conservatism. Dividing the cylinders rated fill pressure (4,500 psi) by the ACR (140 psi per minute), we see that this cylinder will last this firefighter 32 minutes. The formula remains the same for all cylinder sizes.

ENHANCING MEMBER SAFETY

Now that we have the air-consumption rates, we can address air-management procedures. In a large area or office high-rise search operation, the entry officer can monitor the search team’s air consumption by knowing the type of cylinders the team is using and the consumption rates, and using a stopwatch. The turnaround time for the team is determined by the team member with the highest rate of consumption. For example, one member of the search team has a consumption rate of 150 psi per minute and the other 100 psi per minute. The controlling parameter here would be the member with 150 psi per minute. Turnaround time to begin exiting on a 4,500-psi cylinder will be determined by calculating how long the cylinder will last (4,500 divided by 150 psi equals 33 minutes). With this data, the officer can set an appropriate time for penetrating, exiting, and leaving a reserve of air for the unexpected. In this case, the officer could use the rule of thirds used by divers in the overhead environment: one- third of our air supply in, one-third out, and one-third for emergencies. In the above example, this would be 11 minutes in, 11 out, and 11 for emergencies.

If you find this too conservative, you could employ the one-half time plus five minutes method. To accomplish this, subtract 5 minutes from 33, giving you 28 minutes. Half of this is 14 minutes. For this operation, your team would penetrate for 14 minutes and then turn for home. This leaves a five-minute air reserve time. Of course, you can use any conservative number for the emergency air reserve. The point is that you now have a plan based on your firefighter’s air usage.

Another method you can use in bread-and-butter operations is to notify the interior teams at predetermined times, such as in time intervals of eight minutes for 45-minute cylinders. This can also be done in conjunction with a PAR (personnel accountability report).

On getting the transmission, each member would check his remaining air. If he cannot see the pressure gauge, the entry officer would still have a pretty good idea of the air supply remaining for the firefighter. More importantly, the entry officer can order the team to begin its exit at a predetermined time limit, allowing for an air reserve should the unexpected occur.

Air management using air-consumption rates will also benefit rapid intervention team (RIT) operations. Removing downed firefighters is physically taxing and will lead to increased air consumption. Remember, the RIT is there to help alleviate the problem, not add to it.

AIR MANAGEMENT ENHANCES FIREGROUND EFFECTIVENESS AND SAFETY

Officers who know their team members’ air-consumption rates have information that can help them decide when to extend a search and whom to send into certain areas and situations that may require better air consumption. They also can now plan time limits for their firefighters to get out of the building before the low-air alarm activates. In addition, each individual’s knowing his consumption rate makes him aware of how much air remains when the PAR check is given.

• • •

You now have some basic air-management tools and procedures. There is one basic tenet our members should adhere to at all times, and that is to monitor their air supply and not to wait until the low-air alarm is sounding to begin their exit. Too many things can and do happen on the way out.

Endnote

1. Steve Bernocco, Mike Gagliano, Phil Jose, Casey Phillips, “Point of No Return,” Fire Engineering, March 2005.

DOMINICK MARINO has been a member of the fire service since 1975. He is a battalion chief with the Asbury Park (NJ) Fire Department and a volunteer with Manasquan Engine Co. #2. He has been a technical and public safety diver instructor for 23 years. He is also a Pro Board fire instructor.

No posts to display