The Top Ten Chemical Disasters:The recent exposure of 50 workers at the Kaiga Nuclear Power Plant to high levels of radiation highlighted the risks and dangers inherent with using nuclear and chemical technology that is not well regulated or maintained.

Although the latest incident is being viewed as a case of foul play, there have been a number of incidents in the last twenty odd years that remind us that controlling nuclear and chemical technology is a delicate and tricky business, and that if not managed properly, the consequences can be fatal. MSN India takes a look at some of the worst incidents in mankind's history:

Bhopal: the Union Carbide gas leak

On the night of December 3rd, 1984, Bhopal was the victim of one of the worst cases of chemical gas poisoning in history. The Madhya Pradesh city was covered by a poisonous cloud of methyl isocyanate (MIC), which killed 4,000 people instantly and caused health problems for approximately 50,000 people (some estimates range up to 500,000 people). These health problems lead to the death of around 15,000 victims in the following years. According to research done by the BBC in 2004, an approximate 100,000 people still suffer from the consequences of their exposure to gas and a further ten more die every year. This makes the Bhopal gas leak the worst industrial environmental disaster of all time. Today, the location is still polluted with thousands of tons of toxic chemicals, which are stored in open barrels. Rainfall causes the rinsing out of pollution into local drinking sources. According to the BBC, some wells even contain some 500 times the legal limit of the toxins. The victims sued Union Carbide and received a settlement of $470 million.

Chernobyl: Russian nuclear power plant explosion

One of the most famous incidents of its kind, the explosion of the Chernobyl reactor brought home the stark dangers of dealing with nuclear technology. On April 26th, 1986 tests were conducted in nuclear reactor 4 of the Chernobyl plant, 80 miles away from Kiev. These tests required parts of the security system to be shut down, which had disastrous consequences.Thanks to errors in the reactor design and misjudgement by personal, energy production levels shot up to ten times the normal level. The extreme pressures caused steam to starting escaping which built up to a massive explosion which blew the roof off the building, started a major fire and forming an atmospheric cloud which contained between 185 to 250 million curies of radioactive material.The fire and explosion killed 31 people instantly and the presence of the radioactive cloud lead to Moscow evacuating over 135,000 people from within a 30km radius of the explosion. Ukrainian government figures show that 8,000 Ukrainians died as a result of their exposure to the radiation during the first cleanup operation. The eventual death toll from the explosion is estimated to be from 30,000 to 300,000 people. However, unofficial figures put that figure closer to 400,000. The government believes that up to seven million people have been affected by the accident. The reactor is currently enclosed in a large concrete 'sarcophagus' which was built to allow the continuing operation of the other reactors in the plant. However, the structure is unsound and is in imminent danger of collapse, releasing a new cloud of radioactive dust into the atmosphere, due to the 200 tons of radioactive material that remains inside the reactor.A new safe confinement structure is being developed, with plans to have it in place by 2011.

Seveso: Italian dioxin crisis

At midday of July 10th, 1976 an explosion occurred in a TCP reactor in the ICMESA chemical company in Medina, Italy. A toxic cloud was released into the atmosphere which contained high concentrations of TCDD, a highly toxic form of dioxin. Downwind from the factory, a number of neighbouring communities were affected, including the village of Seveso, which gave the crisis its name.The media now mentions Seveso along the same lines as Chernobyl or Bhopal, but it is remarkably different in the way the authorities responded to the incident. Due to earlier accidents, the response time was immediate, and authorities were able respond and treat people effectively and quickly. Polluted areas were researched and the most polluted soil was excavated and treated elsewhere. Dioxin's health effects were immediately realised and the victims were compensated. A long term health monitoring plan was put into place due to Sevego victims suffering from a directly visible symptom known as chloracne, but also from genetic impairments.The accident and the immediate action by the authorities lead to the introduction of European legislation that prevented and controlled heavy accidents involving toxic substances. This regulation is known nown as the Sveso Directive. This directive is the central guideline for European countries for managing industrial safety.The most remarkable feature of the Sveso accident is that local and regional authorities had no idea the plant was a source of risk. The factory had existed for more than 30 years and the public had no idea that there was a chance of an accident. To combat this ignorance, the European Directive was created and was adopted by the Council of Ministers of the European Committee in 1982.

The 1952 London smog disaster

In December 1952, there was an unusual episode of heavy smog in London, which lasted till March 1953. The light winds and high moisture content created ideal conditions for smog formation. That winter was also extremely cold which caused an increase in coal combustion and the increase in car travel, which caused a combination of black soot, sticky particles of tar and gaseous sulphur dioxide. This freak occurrence lead to the heaviest winter smog episode recorded.The smog episode killed almost 12,000 people, mainly children, elderly people and people with chronic respiratory diseases. The number of deaths during the smog episode was three to four times more than on a normal day. The deaths were attributed to lung disease, tuberculosis and heart failure. Mortality from bronchitis and pneumonia increased more than sevenfold. Most deaths occurred due to the breathing in of acid aerosols, which irritate and inflame bronchial tubes. The acidity was not measured at the time, but estimates show that pH levels could have fallen to as low as 2 at the peak of the smog episode.The highest death rate recorded was between December 8th and 9th, with an average of 900 deaths a day. In some of the poorer parts of the city, death rates were nine times their normal number. The heavy pollution and the resulting death toll increased awareness of the seriousness of air pollution. The London smog disaster resulted in the introduction of the first Clean Air Acts in 1956.

Major oil spills of the 20th and 21st century

From the end of the 20th century to the 21st century, there have been a number of major oil spills across the world. These have been caused either by naval accidents or during major wars. It is almost impossible to determine how much damage these spills have caused to the environment.One of the worst instances of oil spillage was during the Gulf War in 1991. After the invasion of Kuwait by Iraqi forces, an international force lead by the Americans pushed them back across the Kuwaiti desert. However, as they retreated, the Iraqi forces created two environmental disasters. First they created an oil spill 16 kilometres from the Kuwaiti shore, dumping oil from several tankers and opening the valves of an offshore oil terminus. The second was the setting fire to 650 oil wells in the Kuwaiti desert.Approximately one million tons of crude oil was lost to the environment, creating the largest oil spill in mankind's history. In the spring of 1991, there were still 500 wells burning, and the last was not extinguished till November of that year.The oil spills damaged life in the Persian Gulf considerably, with the poisoned water killing 20,000 seabirds and severe damage to local marine flora and fauna. The fires in the wells released immense amounts of soot and toxic fumes to the atmosphere, which had severe health effects on the local population and biota for several years. The pollution is also believed to have had a possible impact on local weather patterns. This was the worst oil spill in history, but unfortunately, there have been dozens of incidents over the last few years which have all contributed to the destruction of the environment.

The Love Canal chemical waste dump

In the 1920's a company known as Hooker Chemicals had turned an area in Niagara Falls into a chemical and municipal waste dump. In 1953 the site was filled and relatively modern methods were used to fill up the dump and prevent any chemical seepage. A thick layer of impermeable clay was added to seal the landfill closed.A city council near the landfill site wished to buy it for urban expansion. As development continued, the city began digging to lay a sewer line, unknowingly damaging the red clay cap that covered the dumpsite. Blocks of homes and a school were built around the site and it was named Love Canal.Soon residents began noticing strange odours that hung in the air, and unusual seepages appearing in their yards and basements. Children in the neighbourhood began falling ill and women began suffering miscarriages and birth defects.An activist, Lois Gibbs noticed the strange phenomena and began documenting it. In 1978 newspapers revealed the existence of the chemical waste dump and Gibbs began campaigning for the closing of the school. In August 1978 the campaign succeeded and the NYS Health Department shut down the school when a child suffered chemical poisoning.When the site was researched it was found to contain over 130 pounds of the highly toxic carcinogenic TCDD, a form of dioxin. The total of 20,000 pounds of waste present in the landfill contained more than 248 different species of chemicals. The waste consisted of mainly pesticide residues and chemicals weapons research refuse.The landfill seepage had affected over 900 families, with the chemicals entering homes, sewers, yards and creeks. Eventually, the U.S. government agreed to relocate the families to a safer area. Hooker Chemical's parent company was sued and settled for 20 million dollars.None of the chemicals have been removed from the dumpsite, it has simply been resealed and the surrounding area cleaned and declared safe. Hooker's parent company paid an additional 230 million dollars to finance the cleanup. Today, the Love Canal dumpsite is considered to be one of the major environmental disasters of the century.

The Baia Mare cyanide spill

Workers in gold mines use cyanide to purify gold from rocks. This was applied in a mine in Rumania on January 30th, 2000. However, the cyanide used overflowed into the river Somes and subsequently into the Tisza. The spill was caused by a break in the dam that surrounded the settling basin. This spill resulted in the release of at least 100,000 cubic metres of cyanide laced water into the rivers. The waste water also contained high amounts of heavy metals like copper, zinc and lead. Due to the lethalness of cyanide, Rumanian authorities immediately issued an alarm which prevented any human fatalities. However, the spill did decimate all aquatic and plant life for dozens of miles downstream, affecting the local fishing industry and preventing local residents from access to clean drinking water. The spill reached as far as the Danube in Hungary and Serbia with residents along the riverbanks noticing water full of dead fish flowing by. Up to 100 people, mostly children were hospitalised after eating the contaminated fish.

The European BSE crisis

Bovine Spongiform Encephalopathy is more commonly known as "Mad Cow Disease", and is caused by feeding cows with meat and bone meal, a high protein substance obtained from butchered sheep and cows. It was applied in Europe due to the difficulty of obtaining soybeans, the main ingredient of regular cow feed.The disease spread in Britain due to a lack of proper sterilization techniques which gave a chance for the infectious agents to spread. Although by 1996 there was a ban on British meat exports, it was too late to stop the spread of the disease. In 1996 it was also discovered that there was a human equivalent to BSE, which attacked the brain, causing depression, coordination problems, memory loss, mood swings, pain in the limbs, bad headaches and many other problems.Creutsfeldt Jacobs Disease (vCJD) had killed nearly 90 people in the UK by 2003, with deaths also reported in France and Italy. By 2004 a total of 158 people had acquired or died from vCJD, most of whom were Britons. The incidences of the disease are relatively small in number, but the discovery of it had a dramatic effect on European beef consumption. Even after the BSE epidemic is under control, people are still being diagnosed with its human equivalent every year, due to its long incubation period. The full extent of the outbreak may still be unknown

Spanish waste water spill

On April 25th, 1998, the dam of the mining residual tank of a pyrite mine in Aznalcollar, Spain, ruptured, releasing sludge and contaminated wastewater. The wastewater entered the Guadiamar River, polluting it with heavy metals like cadmium, lead, zinc and copper. The affected area was 4,634 hectares, contaminating 2,703 hectares with sludge and 1,931 with acidic water.The river pollution caused devastation to cultivated lands and forests. Harvests were no longer fit for consumption, causing financial problems for farmers in the area. Fish stocks were wiped out as well, and a number of birds died from consuming the polluted fish. It took more than a month for the river to return to its normal state.Once the river was contaminated, the Spanish authorities reacted quickly with a major cleanup operation, which included the installing of walls to prevent further spreading and to remove the contaminated sludge. The pH values of the soil were restored by liming and arsenic was removed by adding iron oxyhydroxides, causing a precipitation reaction.The company owning the mine stated that the rupture of the residual tank was caused by a deep landslide, which caused a certain section of a wall to move. Authorities concluded that the damn was of weak construction and that warnings of a possible break were ignored. The Canadian/Swedish Company in charge of constructing the dam was charged with financing the cleanup operation and paying compensation to the victims.

The Three Mile Island near nuclear disaster

During the early morning on March 28th, 1979, the main feed water pumps in the non-nuclear cooling system of reactor 2 of the Three Mile Island nuclear power plant failed, leading to cooling water draining away from the reactor, resulting in a partial melting of the reactor core. Operator errors, a stuck valve, faulty sensors and design errors all combined to result in a release of approximately one thousandth as much radiation as during the Chernobyl explosion.Fortunately, the containment structure of the reactor held, trapping inside the 18 billion curies of radiation that could have been released. This proved to be a fortunate escape, as further investigations revealed that a complete melt down was only avoided by the immediate implementation of safety measures.It is estimated that around 2.5 million curies of radiation were released into the surrounding areas. As a safety precaution, all pregnant women and children were evacuated from an 8km radius of Three Mile Island. It is believed that radiation from the accident has contributed to the premature deaths of some elderly people in the area. Dairy farmers reported the death of their livestock and there has been a spate of local residents developing cancer. The reactor clean up began in August 1979 and finally finished in December 1993 at a cost of approximately 975 million dollars. From 1985 to 1990, almost 100 tonnes of radioactive fuel were removed from the site. Although there has been talk of building new reactors, any plans that have been submitted have been dismissed as being too unsafe.