Air Monitoring 101

Hazardous materials incidents remain one the most complex calls that the fire service can Dr. David Greene run. We typically are receiving very limited information and have to use the clues we find on arrival, along with our reconnaissance efforts, to piece together what the problem is. We typically can use our air monitors to assess the severity of the hazardous materials release. However, it requires that we prioritize what it is we are looking for and that we have access to air monitors that are capable of detecting the various hazards.

Monitor for Radiation

First, we want to monitor for the presence of radiation. Radiation is the first priority because we have no defense against it. Rather, our only defense against radiation is time, distance and shielding. Recall that there are four types of radiation: Alpha, Beta, Gamma, and Neutron. Alpha particles travel only a few inches — unless they are dispersed — are easily blocked by skin and are mainly inhalation and ingestion hazards. • Beta particles travel a few feet in the air, can penetrate the skin by a few millimeters (causing

“beta burns”) and can be easily blocked by a thin sheet of metal, plastic or a block of wood. • Gamma rays can travel long distances and are only blocked by very dense materials — lead, large amounts of water, etc.

Gamma rays destroy cells as they penetrate the body. • Neutron radiation is present only when a fission/fusion reaction has occurred (a nuclear device has detonated or inside a nuclear reactor). Neutron radiation normally decays very quickly (sometimes in fractions of a second), which makes our primary concerns Alpha, Beta, and

Gamma.

If we park 100 yards away from a tractor trailer that is involved in a motor vehicle collision and our radiation detectors are giving us readings above background levels, we would assume that it is Gamma as it is the only radiation type capable of potentially travelling 100 yards. If there has been an explosion or fire, we may assume that Alpha or Beta particles have been distributed in the atmosphere, until our air monitor tells us otherwise. In the absence of Alpha and Beta particles, we need only worry about Gamma rays. This is where our time, distance and shielding defense comes into play. If our radiation detector reads “25 R/ hr,” that would be 25 REM (Roentgen Equivalent Man) per hour. That means we have to be there for an hour to absorb 25 REM. The solution is that we don’t stay there an hour. We do what we need to do (i.e., grab the patient) and get out, using time as our friend.

The inverse square law tells us that if we double the distance from the source, we reduce the amount of radiation by a factor of four. So, if we were reading 25 R/hr at 10 feet, we can move to 20 feet from the source and only be exposed to one-quarter of 25 R/hr (6.25 R/hr). Distance is our friend as well. Shielding is difficult to find as we do not normally travel with very dense materials on our trucks. However, our trucks themselves (filled with water) can provide us some protection.

Consider Corrosivity

Next, we need to consider corrosivity. Why? Because corrosive vapors can destroy our air monitoring equipment and cause them not to detect everything else we are worried about. My department monitors for corrosivity using a very high-tech device. It’s called a broomstick. A piece of pH paper is attached to the end of the broomstick which our entry teams hold out in front of the air monitors. A change in color on the

see AIR MONITORING 101 page 25