Radiological Incidents

Radiation

Corrosivity

Oxygen Concentration

Flammability

Toxicity

There are four types of radiation that we may encounter.

Alpha Radiation

Alpha radiation is a relatively large, slow-moving particle that can be stopped by clothing, paper or skin.

Beta Radiation

Beta radiation is also particulate in nature, but is smaller than alpha radiation and travels farther and faster. Beta radiation is stopped by several millimeters of aluminum.

Gamma Radiation

Gamma radiation — unlike alpha or beta — is not particulate in nature but exists as a wave similar to an x-ray. Gamma radiation can travel great distances and is stopped by an adequate thickness of lead — similar to a lead apron being utilized when x-rays are being taken in a dentist’s office. Neutron radiation is not of huge concern to emergency responders, as it normally exists within the containment housing of a nuclear reactor. When responders are asked what type of radiation we should most be concerned with, many responders will answer “gamma radiation.” While we should still be concerned with gamma radiation, the fact is that alpha and beta radiation pose a great threat to responders due to their particulate nature in that they are like dust and can be inhaled or linger as surface contamination.

We should all be familiar with the three tenets of radiological protection — time, distance and shielding. In simple terms, we try to spend as little time in the area of contamination as is possible. We try to place as much distance between us and the radiological source as is possible — “getting some yonder” as some may say. And, we try to place something substantial — a brick wall, fire apparatus, etc. — between us and the source. Many responders also ask about the level of protection that structural firefighting gear provides. If the entire “ensemble” is worn — coat, pants, boots, gloves, hood, helmet, and SCBA — turnout gear usually provides protection from alpha and low-level beta sources.

Now that we have discussed the basic radiological principles, let’s discuss the units of measure we utilize in radiological monitoring. Exposure to gamma radiation is measured in roentgen (R). The use of roentgens as a unit of measure is being gradually phased out. The absorbed dose of all types of radiation can be thought of as the energy deposited in a material and is measured in Radiation Absorbed Dose (RAD). Dose equivalence is the biological damage caused in human body tissue, and is measured in Roentgen Equivalent Man (REM). As REM = (RAD)(Quality Factor) and the Quality Factor for beta and gamma radiation is 1, we can state that REM = RAD for beta and gamma radiation. As it is also generally accepted that for human tissue R = RAD, we can make the conclusion that for our purposes R = REM = RAD. This comes into play with most radiological monitoring that we perform, as many of our radiological monitoring devices are utilized to measure gamma radiation. We also may utilize the concept of dose rate, which is the rate at which a dose or dose equivalent is received. Dose rate can be identified by a time unit in the denominator, such as REM/HR R/HR or even mREM/HR or mR/HR (m or milli meaning 1/1000). Our final unit of measure that we will discuss concerns contamination, which is the quantity of radioactive material in a location. Contamination is measured in Counts per Minute (CPM).

Since we have covered the units of measurement, how about the levels of concern for radiation? The “Administrative Limit” or the value at which emergency responders should notify their supervisor is 1 R or REM. The “Turn Back Value” or the value at which we exit the area of exposure is 5 R or REM. As a fatal exposure to radiation — 50 percent mortality rate — is taken to be approximately 400 R or REM, exposure to the Turn Back Value of 5 R or REM only results in 1.25 percent of a fatal exposure. The level of concern for protecting critical facilities is considered to be 10 R or REM, while that for lifesaving activities is 25 R or REM. Voluntary lifesaving activities can be undertaken at levels greater than 25 R or REM, but again that is only voluntary — no responders can be ordered to go into such areas. In terms of contamination, the threshold value is considered to be 300 CPM.

There are many different types of radiation monitoring and detection equipment. Two basic items of personal radiation detection equipment are the pocket dosimeter and the thermoluminescent dosimeter. Pocket dosimeters resemble a large ink pen that is clipped to the clothing of the wearer and are used to detect gamma radiation.

To read the dosimeter, the device is held parallel to the ground and the user sights through the device towards a light source. A hairline indicator traversing a scale gives the responder a visual indication of exposure in R, which as stipulated above is synonymous with REM when concerning gamma radiation. Prior to use, the dosimeter should either be zeroed using a dosimeter charger or the initial value displayed is recorded and then subtracted from the final value to obtain the actual exposure level. While the pocket dosimeter is a direct — reading instrument that can be read in the field, the thermoluminescent dosimeter resembles film badges utilized in hospital settings in appearance and is shipped to the proper authority for evaluation following any suspected exposure. Thermoluminescent dosimeters are also worn on the clothing of the user and detect gamma or neutron radiation.

Other radiological monitoring equipment includes both analog (such as the older Civil Defense and more modern Ludlum series) and digital (such as the Mini-Radiac and Inspector EXP) meters, as well as other meters that can even identify the particular isotope encountered. Such meters should be maintained and calibrated according to the manufacturer’s specifications. The question then arises of how to properly utilize these devices to monitor the appropriate environment.

In terms of monitoring an area for exposure or contamination with a possible source, we would monitor in a sequential manner from the periphery of the area proceeding towards the likely source while noting any rises in readings above background level and especially noting our levels of concern.

When monitoring for contamination during or following an incident, we usually will be monitoring persons or vehicles. When conducting such monitoring, we will cover the monitoring probe with a plastic bag, medical glove, or other suitable cover to prevent the probe from becoming contaminated. If the probe unintentionally contacts the subject or item being monitored, the cover can then be properly disposed of and replaced.

All monitoring should be conducted at a slow and methodical pace to eliminate any confusion as to the area of contamination and the probe should be held from two to three inches from the subject or item being monitored. When monitoring persons, we should monitor from the head downwards (both front and back), paying special attention to the hands and bottom of the shoes, and also any folds in the clothing. When monitoring vehicles for contamination, we should monitor the entire vehicle while paying special attention to the tires and wheel wells, the engine air filter and interior air filter, the interior vents, and interior carpeting.

In conclusion, the “mystery” of radiological monitoring and radiological incident management is in fact not so much of a mystery at all. With proper equipment and training, emergency responders can effectively manage radiological incidents and perform radiological monitoring with confidence and accuracy.

As always, stay safe out there and be sure to visit the North Carolina Association of Hazardous Materials Responders Website at www.nchazmat.com.