In February 2000 a mysterious incident occurred in a scrap metal yard in Samut Prakarn, Thailand. A few persons dismantling a disused equipment started experiencing nausea and vomiting. Some, who held by hand parts of the dismantled equipment, received burn-like injuries.
Over a period of days the symptoms became more severe and ten persons were admitted to hospital. Four died within weeks. A total of 1870 persons, including those standing nearby, suffered from various degrees of similar symptoms. After visits to the site and interrogation of the survivors by the health authorities it became clear that the persons had suffered from severe radiation sickness.
The equipment they were dismantling was a radiotherapy machine used for cancer treatment. The equipment, though no longer in use, still contained powerful radioactive sources. It inadvertently fell into the hands of the scrap metal dealers who had no idea of the potential hazard.
In the process of dismantling the equipment they had received lethal and near lethal ionizing radiation dose. A trefoil symbol on the equipment to warn the presence of radiation meant nothing to them.
That was not an isolated case. Each year the International Atomic Energy Agency (IAEA) at Vienna receives reports from around the world on injuries and deaths due to misuse or accidents involving sealed radioactive sources.

These sources constitute the most important part of radiotherapy machines used for treatment of cancer, industrial radiography ‘cameras’ used for nondestructive testing of welds and pipes, and irradiators for extending the shelf life of fruits, vegetables and spices and for sterilizing medical products.
They contain intense radiation sources which are well shielded and safe when used properly. After the stipulated period of use, safety experts carefully remove the spent sources and return them to designated authorities for safe disposal before recharging the machine with new sources. Though this is generally the case, in a few instances, as with the Thailand one, used equipment end up in scrap yards leading to serious health risks.
Envisaging such a situation the IAEA had, some decades ago, developed a radiation symbol to warn people. The symbol, used world over, contains magenta or black colored trefoils on a bright yellow background. The three arms of the trefoil are supposed to represent the three types of radiation- alpha, beta and gamma emitted by radioactive materials.
These symbols are prominently displayed on radiation equipment and in places where radiation is used, like X-ray and radiotherapy rooms in cancer hospitals. However, experience over decades indicates that this warning symbol has not been very effective in entirely preventing serious accidents of the above nature.
Experts have felt that the symbol has little intuitive value and cannot be recognized by other than those educated in its significance. According to the IAEA, in a survey conducted at an international school, many children mistook the trefoil for a non-threatening propeller. Hence, the Agency, along with the International Organization for Standards has devised a new symbol for sealed radiation sources.
The New Symbol
The new symbol, released on February15, 2007 is more explicit. It depicts, on a red background, a black colored trefoil radiating waves, a skull and crossbones and a man running away from the scene. The radiating trefoil suggests the presence of radiation The red background, skull and crossbones warn of the danger. More importantly, the person running away from the scene suggests the action to be taken- ‘drop it and run’.
According to an IAEA report the new symbol is, “aimed at alerting anyone, anywhere to the potential dangers of being close to a large source of ionizing radiation”.
The symbol has been tested in 11 countries including India with different population groups, age and educational background to ensure that it clearly conveys the message “Danger- Stay away”. It is not intended to replace the existing trefoil symbol, which will be continued to be displayed on the exterior of radiation equipment and in any area where radiation is used.
However, the new symbol is to be displayed prominently on the device that actually houses the radiation sources, so that, even by mistake, if some one attempts to disassemble the device it provides an explicit warning not to proceed any further. In such a case the best course would be to inform the local police and health authorities.
Ms. Eliana Amral, Director, Division of Radiation, Transport and Waste Safety, IAEA hopes that the new symbol will be accepted and applied by governments and industry to improve the safety of nuclear applications, protection of people and the environment.
India has more than 250 radiotherapy machines, hundreds of industrial radiography cameras and a few irradiators.

Though, India has a good record of radiation safety, some accidents have occurred in the past, due to a combination of negligence and ignorance.
Given the fact that many working in scrap yards are illiterates or semi literates, a pictorial message of this type will go a long way in preventing serious radiation accidents. 
Cobalt Machine
A cancer therapy machine (See pic on top) contains as much as 12,000 curies of Cobalt-60. The source, placed in a separate housing in the machine head, is well shielded with high atomic number materials such as lead and depleted uranium so that it poses no hazard to the operator. When the machine is turned ‘ON’ a beam of radiation emerging through an adjustable collimator is directed towards the patient lying on the couch for treatment. 
The machine can be used for 10 to 12 years at the end of which the radioactivity decreases to about 2500 curies. Though it is not sufficient to treat cancer, it is strong enough to deliver lethal dose to a person within a few minutes, if an attempt is made to remove the source from its shield.
Hence, the regulatory requirements in the design, manufacture and use of these equipment ensure “cradle-to-grave” control of these sources. However, breach in the security provisions may lead to accidents.