RADIATION

 

INTRODUCTION

(MOSTLY FOCUSSED ON GOLD MINING IN SOUTH AFRICA)

 

This blog aims to introduce all occupational exposed personnel to radiation, its health hazards and safety precautions. 

All new employees who are or may become occupationally exposed will be required to attend a Radiation Safety Training Course conducted by a Radiation Protection Officer. 

Basic rules and personal protective equipment will be included and practiced to ensure the risk is kept to a minimum. Employees will be required to assist with the monitoring of their exposure, such as wearing TLD badges, air samplers and radon gas monitors. Co-operation with supervisor and laid-down rules is essential.

OBJECTIVE

Radiation protection requires a basic understanding of radiation, knowledge of health hazards, and the application of radiation safety principles.

RADIATION:

Radiation is energy in the form of particles and electromagnetic waves that travel through space. It is also a name given to the energy emitted by radioactive elements such as uranium. Radioactive elements are those elements that have unstable atoms that decay to form other atoms of another element, accompanied by the release of energy in the form of particles and electromagnetic waves. Uranium is one of the naturally occurring elements that are radioactive, and when an atom of uranium decays, it changes to an atom of a different element that is also radioactive. Each radioactive element in the uranium series gives off one or more types of radiation, such as alpha particles, beta particles and gamma rays.

 

 

These are the main types of radiation we are concerned with in our work environment:

 

1) Alpha particles,

    Are positively charged particles that do not travel very far.

    A sheet of paper or the first layer of skin easily stops them. These particles attach themselves to the aerosols.

2) Beta particles, 

    Are negatively charged and can travel a further distance than alpha particles but can be stopped by a few millimeters of most material.

3) Gamma rays, 

    Are much higher energy waves (similar to light) and can travel great distances through the air. Thick shields of metal or concrete can stop them.

 

 

HEALTH HAZARDS:

 

When a person is exposed to radiation, the atoms in the body can be damaged or changed. Large doses of radiation can cause damage that cannot be repaired, as they prevent the body cells from reproducing more cells to replace the damaged cells. The effects of radiation depend on factors such as the type of radiation, the amount received, the rate at which it is received, and the part of the body exposed. The most important effects of radiation are cancer and genetic damage, which leads to hereditary defects.

 

PATHWAYS BY WHICH WE COULD BE EXPOSED TO RADIATION ARE:

 

Penetration:

Exposure to a source with gamma rays, which irradiate the body from the outside.

 

Inhalation:

Radioactive atoms attached to dust in air, and when breathed in, can cause damage to the throat and lung tissues.

 

Ingestion:

Radioactive atoms attached to food and water can entering through the mouth to the stomach, could cause damage to the body cells.

 

Absorption:

Radioactive atoms entering through open cuts and wounds could cause damage to the body cells.

 

SAFETY PRINCIPLES:

 The following radiological controls have been established to limit our risk to radiation exposure:

AREA CLASSIFICATION

Areas are classified according to potential for radiation exposure within that area. They are classified as:

 

Non-controlled area, 

Where the annual effective dose received by workers will not exceed 

1 mSv. All workers will have free access.

Supervised area, 

Where the possibility of an effective dose is between 1 and 5 mSv per annum. Workers to be medically examined and registered.

Controlled area,

Where the annual effective dose is above 5 mSv.

All workers to be medically examined and registered.

Access to the area to be through a clean and dirty side change house.

Personal protective equipment to be issued when necessary.

Active controls required, maintaining exposure at acceptable levels.

 

 

 

OCCUPATIONAL EXPOSURE:

Occupationally exposed workers are employees who have undergone medical examination and are registered as radiation workers.

The medical examination is conducted prior to start working in a supervised or controlled area and at termination of the contract. Annual medical examinations are attended, exposure levels are monitored and recorded, and workers are registered as occupational exposed persons. Only adults are allowed to register (18 years and above). Workers must attend and successfully complete a training course in Radiation Safety Training. 

 

PROTECTION MEASURES:

 

Radiation cannot be seen, smelled or tasted, so it is only the monitoring programmes of Radiation Personnel and the instrumentation that can detect and keep track of our personal doses. Workers must wear the following instruments to monitor radiation levels.

 

TLD badges – for external radiation. (Thermo luminescent dosimeters)

Air samplers – for internal radiation – (long lived alphas from dust),

Radon gas monitor – for internal radiation – (short lived alpha from radon gas).

 

 

SOURCES OF RADIATION UNDERGROUND (STOPES, ETC):

The sources of radiation in the underground environment can vary depending on the type of reef being mined and the quality and quantity of ventilating air. 

Protection from radiation is mostly afforded by good ventilation control. Uranium and Thorium in ore being mined are the origins of harmful radiation, as well as radioactive products produced by Uranium and Thorium. Radon gas is an important radioactive decay product of Uranium and Thorium, as it can escape from the ore into the air and produce airborne decay products. 

Radon has a half-life of 3,8 days before it decays to its daughter products which attach themselves to aerosols.

To Ensure Adequate Air Velocities in Working Places More Ventilating Air Must Be Directed onto The Working Faces by Ensuring That:

 

Strike walls or ventilation curtains are within the required distances from the faces.

Ventilation brattices and doors are installed at the correct positions in dip gullies and travelling ways.

A plug of rock is left in stope ore passes to prevent short-circuiting of air.

Prevent accumulation of rock on the stope faces, causing air restriction

 

 

PRECAUTIONS TAKEN TO MINIMISE EXPOSURE TO INTERNAL RADIATION INCLUDE:

Minimize dust in your workplace by proper watering, washing down and by good ventilation.

If you have to work in an area where dust is inevitable, wear a mask of an approved design and follow the fitting instructions.

It is also important to make sure that any contaminated clothing is removed at the end of a shift and that hands are washed before meals and smoking. At the end of each shift it is necessary for people to shower.

Stope width control: do not leave reef in the hanging and footwall unnecessarily.

Do not leave sweepings in the worked out areas.

Maintain good stope/development end ventilation control.

Do not sprag ventilation doors open which causes short-circuiting of air.

Do no break open walls and seals that allows contaminated air to enter the workings.

Do not enter the worked out areas at all, these must be barricaded off.

 

 

PRECAUTIONS TAKEN TO MINIMISE EXPOSURE TO EXTERNAL RADIATION:

External radiation is radiation that comes from a radioactive source outside the body, usually gamma rays. There are three basic factors that control the amount of exposure a person receives: the length of time they are exposed, their distance from the source, and the amount of shielding between them and the source.

 

Time:

Time is important when it comes to radiation exposure. It means taking breaks away from the source of the radiation, such as taking meal and smoking breaks away from the area where radioactive material is being processed, handled or stockpiled. 

If you spend twice as much time near a radioactive source, you will receive twice as much radiation exposure. This illustrates an important rule.

 

If you work in an area where there is radiation you should minimize the time spent there.

 

Distance:

The inverse square law states that the radiation level falls off as the square of the distance from a radioactive source. This is similar to a fire, where the closer you get to the source, the hotter it is. When radioactivity is concentrated in one small area, the radiation level falls off as the square of the distance from the source. 

If you double the distance from the source, the radiation level falls to one quarter, and if you triple the distance from the source, the level of radiation falls to one ninth.

 

Shielding:

One way of reducing the level of radiation in an area is to place absorbing material between yourself and the radioactive source.

This may be necessary in very special cases, such as when repairing the inside of the Acid Plant Roasters, Swemco Towers or Gas Cleaning Cyclones.

Shielding can reduce gamma radiation. On the plant, the layers of steel or concrete of the vessels containing radioactive material affords some protection from gamma rays.

Tanks, structures and pipework  also provide some shielding effect.

 

 

 

MONITORING:

 

Radiation workers required to enter or work in a contaminated/controlled area, have to be monitored to determine the potential exposure they could receive in such an area.

This monitoring will determine external and internal exposures.

You will therefore be required to wear badges (TLDs), air samplers and radon gas monitors (RGM).

The badges will measure your gamma and beta exposures as you move around the site, whilst the air sampler will collect invaluable dust that will be analyzed by the supervisor to give an indication of the amount of radioactivity that you have inhaled.

The RGM measures the amount of radon gas and thus the amount of radon “daughters” that could be inhaled.