|Many Hazmat Technicians and Specialists make the comment that “I do not do radioactives” — sometimes even with a few unprintable words thrown in. Radiological hazardous materials seem to elicit such a response due to the infrequent nature of responses to incidents involving such materials and the erroneous belief that radioactive materials are a mysterious realm of the hazmat discipline.|
Personally, I would rather respond to a radiological incident rather than one involving an unknown hazardous material or multiple unknown hazardous materials because radiologicals are a known entity in that we know how to monitor for their presence, their relative level of harm, and we know how to protect ourselves from them. Due to the above, it was felt that we should revisit the topic of radiologicals. Additionally, as of late we have been concentrating on management and leadership topics in our discussions so it was deemed that a return to the more technical side of things was warranted.
Different Types of Radioactivity
Alpha and beta radiation is of a particulate nature (e.g. like dust particles). Alpha particles are heavy particles that travel only four to seven inches and can be blocked by clothing, paper or skin. Beta particles are lighter than alpha particles and hence travel a farther distance than alpha particles. Beta particles can be blocked by several millimeters of aluminum. Our structural firefighting ensemble (including SCBA) will actually protect us from alpha and low-level beta radiation. Since both alpha and beta radiation are particulate in nature, they can leave contamination behind. Due to this fact, alpha and beta radiation pose some of the greatest threats to emergency responders of any of the types of radiation.
Gamma radiation, on the other hand, is not particulate in nature but rather travels as a wave much like x-rays. Due to this fact, gamma radiation does not leave contamination behind and can be blocked by lead. Emergency responders do not usually have to be concerned about the fourth type of radiation — neutron radiation — as it is normally only present inside the containment structure of a nuclear power plant during operation. Neutron radiation is blocked by a thick mass of concrete.
As emergency responders, we should all be familiar with the principles of radiation protection that we have been taught since the beginning of our hazmat careers. The first principle is time, meaning we should spend as little time as possible in the area of exposure or possible exposure. Distance is the second radiation protection principle in that we should put as great a distance as is possible between ourselves and the radiological source. The third principle is shielding, as we should put whatever we can in between ourselves and the radiological source to block the radiation as much as possible such as fire apparatus, a masonry wall, or other appropriate objects. This combination of time, distance, and shielding should be ingrained into our hazmat response memories.
Where Are Radiologicals?
We are likely to encounter radiologicals in one of two settings, namely either in transportation or in nuclear power plant response and operations. We will first focus on the realm of transportation. The packaging that radiologicals are transported in is categorized by the Department of Transportation (DOT) into three categories: Industrial, Type A, and Type B packaging. Industrial packaging — also known as strong, tight packaging — is utilized for low-level radiologicals and is designed to withstand normal transportation handling. Type A packaging is designed to withstand normal transportation handling and minor accidents, while Type B packaging is designed to survive severe accidents. Type A and B packaging must meet specified performance-based standards set forth by the DOT.
As we all know, individual packages in transportation carrying hazardous materials are required to have labels affixed to them. Packages carrying radioactives are no exception. Radioactive labels exist in three main categories entitled Radioactive I, Radioactive II, or Radioactive III. These labels not only have distinctive colors — all white for Radioactive I; and yellow over white for Radioactive II and III — but also display the trefoil or “propeller” radiological symbol. The maximum allowable level of activity allowed in each category increases as the Roman numeral designator increases. The contents of the container and the activity level are listed on the label, and for Radioactive II and III labels the Transport Index (TI) is also indicated. The TI equals the radiation level at one meter from the package measured in units of millirems per hour. Any highway or rail mode of conveyance carrying any amount of a Radioactive III substance must be placarded on all four sides with yellow over white placards displaying the word “Radioactive” and the DOT hazard class numeral “7.”
How to Quantify Radiologicals
Prior to transitioning to the setting of nuclear power plant response and operations, let us discuss the measures that we use to quantify radiologicals. Exposure to radiation is measured in Roentgens (R). The biological damage caused to human body tissue is measured in units of Roentgen Equivalent Man (rem). For beta and gamma radiation, one Roentgen equals one rem. Units of time can also be combined with the above units to indicate the dose rate, such as rem/hr or R/hr. Just as in the metric system of length measurement, the prefixes of milli (one one-thousandth) and micro (one one-millionth) may be utilized. For example, in length measurement there are 1000 millimeters in one meter. Likewise, there are 1000 millirems in one rem (or alternatively one millirem equals one one-thousandth of a rem). The level of alpha and beta contamination is measured in units of counts per minute (cpm). In the State of North Carolina, 300 cpm is considered the threshold for contamination.
We must next state that the likelihood of a radiological release from a nuclear power plant is highly unlikely due to the highly regulated nature of nuclear power plants and the redundant safety measures that are in place. Nuclear power plants simply utilize a nuclear reaction to heat water into steam to turn a turbine that is attached to a generator. If responders ever were required to conduct operations at or near a nuclear power plant, however, they should be trained in the use of radiological detection and protection equipment and principles. Personnel entering into an area of possible exposure or contamination would wear a device called a pocket dosimeter on their person that provides a direct reading of exposure levels and is read at regularly specified intervals. Personnel also would wear a thermoluminescent dosimeter (TLD) which is now also known as a personal record dosimeter (PRD) that is returned following the possible exposure and is read after the fact to determine exposure levels, serving as a second source of information regarding exposure levels. Personnel and vehicles exiting the area of possible exposure would also be monitored for contamination, with the aforementioned threshold of 300 cpm existing in the State of North Carolina to denote contamination.
Levels of Concern
The first level of concern for responders to nuclear power plant incidents is the administrative limit of one R or rem. When that exposure level is obtained, the responder must notify their supervisor. One major topic of note is that in the State of North Carolina, the remaining levels of concern for exposure in nuclear power plant response have recently been reduced by half. The turn back value or working limit of two and one-half R or rem is the exposure level at which the responder must exit the area of exposure or possible exposure. Responders may protect critical facilities up to an exposure level of five R or rem. Lifesaving activities can be conducted at up to 12 and one-half R or rem, and voluntary lifesaving activities can be conducted in excess of 12 and one-half R or rem.
As can be witnessed in our discussion above, the supposed mysterious nature of the subject of radiological hazardous materials can be de-mystified through the attainment of knowledge in the topical area regarding radiation detection and protection principles; as well as the recognition and identification of radioactive hazardous materials in the transportation setting.
As always, stay safe out there and be sure to visit the North Carolina Association of Hazardous Materials Responders website at www.nchazmat.com