Industrial radiography – hazards and control
Radiographic Testing - RT
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| radiation |
What is meant by radiography testing (RT)
Radiography is used in industries for indestructible testing of defects in metallic components and weld joints to ensure the safety/durability and integrity of a pipe or another joint. Industrial radiography equipment with sealed radioactive sources emits gamma rays or x-rays. These sources used in radiography testing for high energy, short wavelength and electromagnetic waves.
What is radiation?
Radiations are the emission of an electromagnetic wave or
subatomic particle of energy. Simply we can say that radiation is energy
that is emitted by a source.
When the radiation is stopped by any substance or absorbed
by it, then that substance is called Exposed by that radiation. As the light
falls on us, we are actually exposed to the light. During an X-ray procedure,
the patient is exposed to an X-ray.
The source of natural radiation can be found in outer space
and naturally energy the core of air, water, food and earth.
Radiation can be natural and manmade (Man-made radiation sources are X-ray machines, nuclear power plants, some consumer goods like T.V., Luminous Watches etc.)
Isotope
Isotopes emit uncontrolled energy in the form of radioactive waves which are hazardous to all living things as they can destroy the the living tissues that cause a fatality or can convert it into cancer.
Radiation effect (Radiation hazards)
Radiation hazards depend on:
- The type of radiation
- The energy
- The extent of penetration of tissue
- Duration of exposure
The human body made up of trillions of cells. Every cell contains a nucleus without neutrons and protons. Contain the genetic material in the form of 23 pairs of chromosomes. Each chromosome consists of a single molecule of deoxyribose noetic acid (DNA). Any chemical change in the DNA, the molecule of DNA become mutated. The mutation is the basis for cancer cell formation.
Radiation can be divided into two parts,
1.
Ionizing - (penetrating radiation) When one more electron is removed
from its shell around the nucleus of the atom can cause a positive charge of an
atom. It is referred to as ions and radiation is called Ionization. Because
electrons are negative charge, protons are positive charge and neutrons are no
charge.
So, when ionizing radiation is observed by living tissue
will be converted to ions by the radiation, causes the destruction of DNA
because of high energy chemical reaction in the living tissue. Two basic kind
A. Electromagnetic (X-ray, Gama ray), Gamma – caesium 137, Delta 60 and Iridium 192 used in industrial radiography
B.
Particulate radiation (Alpha-beta, neutrons)
Alpha - less penetrating than gamma rays, only capable of
more in air and unable to penetrate even paper such as smoke detector. Uranium
238 is an alpha particle.
Beta – beta is more penetration than Alpha but less than
gamma. They can pass through paper or skin.
Neutron – Neutron is the most penetrating than Alpha and
Beta. They can pass through tissue even concreate
2.
Nonionizing - This is the type of diffusion that
does not produce ions
- Ultraviolet (sunlight, welding)
- Visible (sunlight, laser, arc welding)
- Infra-red (hot object)
- Microwave
- Radio wave (satellite communication, TV, radar, MRI, medical diagnosis)
- Electromagnetic radiation - heat, radio waves, visible light, x-rays, etc.
What is a decay chart?
It is the chart showing the change in radioactivity of a
source, for a period, at a regular interval of time. Example source is 1000 query,
after 75 days it becomes zero, does not matter it is being used or not.
Hazards:
Acute radiation sickness – massive cell death caused by direct damage to the DNA cell.
- Nausea and vomiting
- Diarrhoea
- Fever
- Hair loss
- Headache
- Skin burn
- Death (high dose)
- Anaemia
Chronic effect:
- Cancer
- Genetic damage (parents to offspring – sterility, heritable a genetic defect in children)
Control measure:
1. Minimize Time
The dose of any person is directly related to their exposure time. If someone's exposure time is doubled, then his exposure will also be doubled. Exposure time is kept low during the radiograph. Radiation doses can be directly worked by reducing exposure time. The absorbed dose increases with time and the absorbed dose decrease with decreasing time. Radiation dose can be reduced by reducing the time of radiation expo
Increasing the distance between a radiation source and reduces
radiation exposure rapidly. Always keep yourself (the authorized crew who is involved in radioactivity) outside the controlled area where the radiation dose
is more than 0.75 mRem/h (7.5 microsieverts and the public follow the supervisor
area (2.5 mRem)
2. Maximize Distance
By shielding between an exposed person and radiation source
from radiation, the radiation dose can be reduced drastically Shielding of lead and
lead equivalent material is an effective way to protect against x-ray and gamma-ray radiation. Lead aprons, mobile lead shields, lead glasses, and lead
barriers etc. are various types of equipment used in shielding. It is necessary
to use these shielding materials while working in the radiation area.
3. Work Permit
A work permit to minimize the exposure to any radiation amount
and risk associated with it. And also, to define safety requirements for
working with or near radioactive source equipment. This permit applies to all
employees and contractors who design, specify, order, purchase, receive,
install, move, relocate, store, ship and work in the vicinity of any equipment
containing radioactive materials of any amount using Radiation. The radiation safety officer (RSO) is responsible for the survey of radiation level around
the sources and whenever it is required during NDT, to safeguard the safety of
the personnel, and is responsible for maintaining.
4. TLD badges (film badge)
This badge will be worn by personnel, exposed to radiation
due to their nature of duty and this is processed to calculate the received radiation dose of a person during the period (normally 1 month) of exposure. Thermo-Luminescent
Dosimeter Shall be established in locations where the worker may be exposed to a dose
limit greater than 3/10 of the occupational exposure limit (3µSv/h).
5. Electronic personal dosimeter (EPD)
response to gamma, beta, alpha and X-
radiation used to calculate the received radiation dose of a person during the
period (normally1 day) exposed to dose limit (0.75 mRem)
6. Radiation Survey Meter (Geiger meter)
It is the instrument used to measure the radiation dose of the surrounding where the radiation test (RT) is going on.
7. Barricade the work area
The controlled area is calculated, evacuated and the supervisor
area should be barricaded with yellow/black tapes, warning signs (a minimum of
4nos.), and red or yellow flashlights should be posted.
8. Training
No person may engage in any activities involving radiation
exposure before receiving adequate training on such activity, gaining knowledge
of the methods and criteria of protection from radiation and methods of safe
work. Therefore, only the authorized worker can work in the same area. Only
authorized workers can handle the radioactive sources,
OSHA standard 1926.53
