Wednesday, 23 September 2020

ALARA in Controlling Radiation Risks in the Industries


Industrial Radiography is a non-destructive testing method to check for defects (e.g. Cracks, lack of penetration, porosity, inclusion, pinholes) in pipes, pressure vessels, valves to ensure quality /durability in the metal products. With Radiography, we get information inside the metal just by taking a picture of it without breaking it or spoiling it to evaluate the structural integrity or find out the hidden details of an assembled structure. Since this method uses ionizing radiation, it is important to ensure not only the quality of product, but also the safety of the technician and the general public, as well as the protection of the environment. Since the technique deals with very large amounts of radiation during testing periods, improper practice could result in the technician and the public being exposed to a large dose of radiation in just a few seconds. Therefore, a high degree of care and professionalism is required for radiography work. Moreover, contamination from a corroded or damaged source can cause additional radiation hazards to radiography personnel.

The radiography procedure for a work activity must be developed in such a way that only a minimum dose is received during practice. This is achieved through the proper design of radiography exposure installation, proper training of radiation workers, strict adherence to radiation safety rules and proper selection and maintenance of radiation sources. The industrial radiography devices are commonly called as cameras. They are either Gamma cameras or X-ray cameras.

Radiation Exposure risks

Overexposure to ionizing radiation is harmful as it may cause cell damage to the exposed person. People are constantly exposed to a certain amount of radiation from natural and man-made sources. The intensity of radiation hazards is decided by several factors, such as their physical form and activity, energy, radiation type, etc. All radiation related hazards can be broadly classified as either external or internal hazards. External hazards are radiation from outside the body, while internal hazards arise when sources enter the human body and start irradiating at the place of their residence. Radiation hazards in industrial radiography are mainly caused by external sources, as x-rays and gamma rays are penetrating in nature and can irradiate organs deep inside the body. Therefore, radiation hazard evaluation is necessary in order to avoid alarming levels of exposure.

Radiation Protection and Dose Limitation

The International Committee on Radiation Protection (ICRP) has framed a set of guidelines for arriving at dose limitation:

Doses received during radiation work should follow the ALARA principle: As Low as Reasonably Achievable.

The Dose limit should not exceed prescribed limits.

The annual dose limit should be designed in such a way that it prevents detrimental effects and limits probabilistic effects. 

ALARA is an acronym used in radiation safety for “As Low As Reasonably Achievable.” The ALARA radiation safety principle is based on the minimization of radiation doses and limiting the release of radioactive materials into the environment by employing all “reasonable methods.” ALARA is not only a sound radiation safety principle, but it is a regulatory requirement for all “radiation protection programs.” The ALARA concept is an integral part of all activities that involve the use of radiation or radioactive materials and can help prevent unnecessary exposure as well as overexposure. The three major principles to assist with maintaining doses “As Low as Reasonably Achievable” are time, distance and shielding.

Radiation protection principles

The principles of radiation protection include:

1.    Time - The shorter the time spent close to the source, the lower the radiation dose that will be received. Limiting the time of radiation exposure will reduce the radiation dose.

2.    Distance - The intensity of radiation falls off sharply as a person moves farther away from the radioactive source. Increasing the distance between the person and the radiation source will reduce exposure.

3.    Shielding - The thicker the protective material placed between the person and the source, the less the amount of radiation a person will receive. Lead or lead equivalent shielding for X-rays and gamma rays is an effective way to reduce radiation exposure. There are various types of shielding used in the reduction of radiation exposure including lead aprons, lead glasses and lead barriers. When working in radiation areas it is important to use shielding whenever possible.

Means of reducing internal radiation exposure

1. Practice good Hygiene

Practicing good hygiene and housekeeping habits effectively moderate the internal radiation hazards presented by radionuclides. By eliminating the presence of food and drink in areas where radioactive materials are used or stored, and controlling “hand to mouth” habits, the risk of internal radiation exposure is reduced.

2. Control of Contamination

Labeling radioactive and potentially radioactive areas and items will help prevent the spread of contamination. It is important to control contamination with absorbent papers and spill trays and placing any contaminated item in a properly labeled waste container. When a contamination occurs it is important to promptly decontaminate the area to prevent the spread of the contaminate.

3. Airborne Hazards

Using fume hoods and avoiding dust, aerosol, or volatile gas production can reduce the potential for inhalation of radioactive substances.

4. Use Proper PPE

Using the proper personal protective equipment (PPE) such as disposal gloves, lab coats and glasses etc. will help reduce the possibility of ingestion or absorption of radioactive materials.

Radiation safety monitoring equipment

Radiation monitoring equipment must be used to measure radiation doses. This equipment includes personal dosimeters, direct reading dosimeters, personal alarming dosimeters and radiation survey meters.

Personal dosimeters
Personal dosimeters are passive dosemeasuring equipment; the most commonly used being a thermoluminescent dosimeter (TLD) or an optically stimulated luminescence dosimeter (OSLD).

Direct reading dosimeters
A direct reading dosimeter (DRD) is a real-time dosimeter that monitors the absorbed dose to the worker, and is checked periodically by the radiographer during the shift, to verify doses received during radiography work.

Personal alarming dosimeter
A personal alarming dosimeter emits an audible warning signal when a dose rate alarm set point is exceeded.

It’s very important to understand how to protect the workers when working around high frequency radiation and to be aware of ways to reduce the level of radiation exposure. It takes a team effort to successfully implement the ALARA principles and make ALARA a routine element of work in radiological areas.

Article by Dr.Yashoda Tammineni,
MSc, Ph.D.

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