Radiation Safety for HVAC Engineers and Technicians
HVAC experts should know something about radiation and it’s control for a variety of reasons. First, planning and designing effluent systems for laboratories and other industrial facilities requires some knowledge of this hazard and how it is used. Secondly, maintenance and repair of these systems will require some near contact with potentially contaminated components such as fume hoods, blowers, flow dampers and ductwork. Finally, the rare need to dismantle these systems will require specialized knowledge, training and contractors to properly and legally dispose of the system components contaminated by radioactivity.
Although, some engineers and technicians may have acquired an understanding of radiation from their education, it is a rather specialized field. Don’t feel singled out if your knowledge is zero or based on hearsay. You’re not working in a vacuum because experts in radiation safety are available to help you.
Radiation safety specialists are known as “health physicists” and “radiation safety officers.” If the institution that you are working for already uses radioactivity on site, they must by law have a designated radiation safety officer or “RSO.” The institution will also have a radioactive materials license from the Nuclear Regulatory Commission or a state agency with equivalent oversight. The RSO makes sure that regulations are followed concerning the proper use, control and management of the radioactivity. Why all the legality? For one reason, radiation is a potential hazard that requires a separate waste disposal route. Mixing it with other waste streams, particularly metals and standard trash, is not permitted. For another, radiation safety is historically connected to a federalized system of regulations that paralleled nuclear reactor development and research into radiation effects. Radiation safety regulations tend to be uniformly applied across the nation (after September 11th, some regulators have seen a need for tightening certain of these restrictions).
Institutions using radioactive materials will have a radiation safety program in place commensurate with the amounts and types of radioactive isotopes in use. Regulating agencies periodically audit radiation safety programs to verify compliance with the radiation safety code. Such safety programs always make provision for periodic inspections by the RSO of facilities within the institution where radioactivity is used. Almost always, radiation measurements are made during these inspections in an effort to control contamination in the workplace. Therefore, knowledge of contamination levels at specific plant locations can be obtained from the RSO. He or she must also document that plant personnel are obeying radiation safety regulations. The RSO will know what radioactive substances have been or will be used in an air effluent system. If contamination levels in the system are unknown, he or she can perform measurements to have that determined. If the air effluent system had to be licensed with state regulators or the NRC, the RSO will already be maintaining a database of total radioactivity amounts released at the stack. Other related data such as airflow rates and airflow calibration data will also be on hand. Therefore, the RSO is a source of information that HVAC- and other contractors can tap to do their jobs safely and effectively.
Smaller institutions may not have a full time RSO. An employee with some interest in radiation or in some cases, just a scientist-volunteer may be handling the day to day administration of the radiation safety program. Under these circumstances, many regulatory agencies will require that a health physics consultant be maintained by the institution to provide technical and regulatory assistance. Health physicists (HPs), especially the consulting variety, are often certified by the American Board of Health Physics to indicate that the individual has tested successfully at a certain level of competency. Even with a certification, an HP with some ventilation design experience will be more useful than one with none. This individual would be the one to contact for a special project involving the fume hood air effluent system (covered below). Though the RSO or HP may have the answers you need to do your job, it doesn’t hurt to know a little bit about radioactivity yourself.
What about radioactivity?
Radioactive elements undergo a spontaneous transformation into another element. Sometimes the product element is also radioactive and the transformations will continue until a non-radioactive (stable) element is created. Every transformation of a radioactive atom is accompanied by the release of radiation. Depending on the element, the radioactivity may be a sub-atomic sized particle like an electron (a beta particle), a combination of 2 neutrons and 2 protons bound together (collectively called an alpha particle) or the radiation may be a non-particulate “ray” as in a gamma ray or X-ray. Radioactivity is the process of emitting radiation.
Each of the radiation types have certain qualities that are important to safe handling of equipment that may be contaminated by radioactive elements. Alpha particles, for example, which do not have any significant range in air, are not considered “penetrating” radiation. However, they can still irradiate sensitive human tissue if brought into contact with it. The best example of this situation is the inhalation of respirable dust contaminated with alpha particle emitting radioactive elements.
Beta particles, being smaller and less massive than alpha particles, have a longer range in air. Depending on the radioactive element, which determines the energy of the beta particle, a significant radioactive dose to the skin from this type of radiation may be possible. Some radioactive elements like phosphorous-32 emit beta particles with a range of about 20 feet in air. Fortunately, steps can be taken to reduce the hazard such as using protective clothing. Pre-cleaning of contaminated areas can also be performed, especially if dismantling or plasma-cutting are planned. Even delaying work, to allow natural radioactive decay to reduce the exposure rate, may be helpful.
Gamma-emitting contamination is another matter. Since they are massless waves (or packets) of energy, gamma-rays (and X-rays) don’t interact with materials very efficiently. Since they are not deflected or stopped very well except by dense materials like lead, they tend to have long ranges of many feet in air. This characteristic of gamma radiation will hopefully have been considered in the design of any ductwork that handles such contaminated effluent. The RSO will have to make an exposure assessment by taking measurements to determine if work can be done near or on gamma-contaminated air moving equipment. Iodine-125 is a typical gamma-ray emitting radioactive “isotope” that HVAC experts might encounter because it is often filtered from effluent air by using activated charcoal bag-out/bag in systems.
The health and safety issues of radiation usually deal with minimizing the exposure to radiation either from direct contact or externally from radiation emitted over a distance. Personal protective equipment such as disposable coveralls, hair covers, shoe covers, gloves and eye guards are standard precautions that provide basic contamination protection from radiological, chemical and biological hazards (up to a point). The use of a respirator may also be necessary if the RSO is concerned that the radioisotope is, or will become, airborne.
“T-D-S” or time, distance and shielding comprise the three fundamental principles of radiation safety. Minimizing the time spent around a source of radiation will minimize the total exposure that a worker will accumulate during the job. Radiation monitoring devices such as Geiger counters are calibrated to measure gamma radiation exposure rates, not total exposure. Many radiation safety regulations are also stated as exposure rates. Therefore, RSOs are motivated to reduce these rates, or if they cannot, to keep the working time in proximity to sources of radiation as short as possible. This is always a compromise, because recklessly hurrying through a job can create an accident that may lead to a mechanical injury and perhaps to a higher than expected radiation exposure.
Maximizing the distance between the worker and the source will also keep the total dose low. The exposure rate of the radiation will decrease as the square of the distance between the source and the person. So, doubling the distance reaps a health and safety bonus because the exposure will decrease to
The application of shielding to a source will reduce exposure rates if done properly. However, shielding may not be possible to use in situations involving HVAC work. For low energy beta-emitters, the materials comprising the duct work (metal), the filters and any other materials used for handling filters (plastic sheeting), will provide some shielding from this form of radiation. Gamma-rays and higher energy beta particles may be scattered by these materials but will not be stopped.
Radiation doses to personnel trained in the hazards of radiation (radiation workers) must be legally maintained below prescribed levels. Reaching these limits is not considered good practice but it is also not a serious health issue. Annual low level doses of 1/10 to 1/100th of the whole body limit of 5000 mrem are routinely encountered by medical radiology personnel, scientific researchers, and nuclear power plant workers. Though well-run radiation safety programs throughout the world strive to keep personnel doses as low as reasonably achievable (costs and other social factors taken into account), no significant health effects from intermittent occupational radiation exposures at the fractional levels mentioned above are observable. HVAC work and radiation
The RSO’s role or that of the health physics consultant will change depending on whether a new air effluent system is to be installed, or if an old system is to be dismantled and scrapped. In all cases however, the RSO can provide basic on-site radiation safety training to HVAC techs and engineers and describe the specific use and hazards of the air effluent system. Radiation monitoring devices to measure personal doses can also be obtained from the RSO.
New Installations. Fume hood and duct work installations for use with radioactive effluents will require less participation by the radiation expert than the scrapping of a contaminated system will (see next sub-section). The RSO or HP can provide advice about hood materials, required fume hood face velocities, the need for fan-failure alarms, the need to maintain a supply of fan and motor parts, filtration requirements if any, and stack heights and stack placement. For many laboratory applications, special materials like stainless steel are not required. Decontamination of low level radioactivity on accessible surfaces usually only requires an impervious, smooth surface. The chemicals used with the radioactivity would have more of a bearing on the choice of materials. Although not a necessity, if inner surfaces can be detached with relative ease from the hood frame, disposal of permanently contaminated surfaces becomes easier. Special, high flow rates for most lab uses of radioactivity are also not required. Face velocities of 60 to 100 fpm (sash fully open) are adequate recognizing that room air patterns and sash heights effect hood performance.
The RSO must also determine whether the emission point will need a special permit from the regulatory agency with jurisdiction. The permit will have to be obtained using plans and ventilation calculations provided by the HVAC engineer so that effluent discharges can be estimated for review by the regulating body. That information will be used to set discharge limits for the radioactivity. The RSO must then assure that the permit limits are met. Periodic reporting of effluent totals to plant management and the regulating agency is usually required.
Maintenance. If the effluent system is issued a permit with an annual discharge limit for radioactivity, then the volume flow rate of the system will have to be measured periodically. Sometimes the RSO can do this or perhaps an HVAC specialist with the expertise to take Pitot tube measurements will be contracted. The stack flow rate is needed by the RSO to calculate the total radioactivity emitted by operations in the hood. The RSO should do a post-job survey of the air flow measurement equipment used inside the ductwork by the HVAC specialist in case decontamination is required.
If the fume hoods are used for relatively high levels of airborne radioactivity, the RSO will demand that low-flow alarms be installed to warn the hood users of a blower failure. Under failure mode, the users would cease work, close the hood sash to encourage natural chimney effect flow (if present) and depart the lab. Without the alarm, work might continue with inadequate face velocities possibly resulting in the inhalation of radioactive materials.
The change out of bag in/bag out filter cartridges designed for the removal of radioactive air effluents is a situation in which the HVAC tech or engineer is brought in close proximity to radioactive materials. As mentioned earlier, charcoal filtration is used to trap radioactive isotopes of iodine, an element used in biological and pharmaceutical research. Elemental iodine and some compounds like sodium iodide evaporate easily so as to be present in the work-zone air necessitating use of a fume hood. Because this isotope emits gamma-rays, the RSO must be contacted to do an exposure rate survey of the filters prior to change out. If the exposure rate is high, the RSO may wish to delay work to allow for radioactive decay. The total exposure received by an HVAC tech should be restricted to a small fraction of the annual limit permitted to radiation workers if the filter change is planned properly. The RSO should oversee the change-out operation even though the bag out system limits actual contact with the contaminated filter.
Scrapping Used Systems. It is not unheard of to “decommission” radiochemical laboratory rooms or entire buildings that contain such labs. To meet the limits legally set for decontamination efforts, surveys must be done using appropriate radiation detectors in order to first find the contamination and then to clean it. These go beyond the routine surveys RSOs carry out periodically. Now, radioactivity on all surfaces such as walls, ceilings, casework, floors and in effluent ventilation systems, must be measured and documented especially if the buildings or rooms are to be turned over to “unrestricted use” (use by the general public).
Radioactive duct work, blowers, dampers and other components will require decontamination or removal to meet decommissioning goals. The contaminated components that cannot be cleaned will require packaging and hauling to a licensed radioactive waste processor. Radioactively contaminated metals must never be mixed with clean metals %%MDASSML%% especially if there is a chance the metal will be recycled. Radioactive waste management is a significant fraction of the total cost of a lab or building decommissioning. It involves the packaging of the waste, it’s manifesting, transportation, and final disposition. Components or material that are not contaminated by radioactivity can be segregated and disposed of by general means so long as biological and chemical decontamination, if needed, has occurred.
Such decommissioning projects are beyond the capabilities of most plant RSOs, even those with large staffs of assisting health physicists. The job will usually be contracted out to a company with radiological decommissioning experience. The decommissioning firm will work with the site RSO to provide assurance that decontamination, dismantling and radiation measurements meet the decontamination acceptance criteria of the regulating agency. Such firms will decontaminate or remove the hoods, duct work, stacks and blowers if need be, as part of the overall room or building decommissioning. Ducts can be cut with plasma torches and removed a piece at a time. Roof mounted blowers may require a crane to bring these units to ground level.
Where to Learn More
A great, concise, easy to read book about fume hoods written by an expert experienced in radioactive work is Laboratory Fume Hoods by G. Thomas Saunders (John Wiley & Sons, 1993). The author provides practical knowledge and dispels many myths about hoods in general and about fume hood use with radioactivity in particular.
The Eagleson Institute, a non-profit foundation interested in laboratory safety, provides seminars, conferences, training videos and web-based software on biological safety cabinets and chemical fume hoods. An Eagleson session entitled “Safety Issues for Certifiers: Radioactivity and Potent Compounds” was held recently at the 11th annual meeting of the Controlled Environment Testing Association (CETA). The web-site for Eagleson is www.eagleson.org and that of CETA is www.cetainternational.org .
The Health Physics Society is the professional association of RSOs and similar radiation safety specialists. On its web-site, you can find basic information about radiation and even ask a technical question that will be answered by a real health physicist. Go to www.hps.org .
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