The chemicals used in projects to reduce rainfall pose no danger to people or the environment, the head of the Beijing weather modification department said Thursday.

Since 2002, the city's meteorologists have been experimenting with rain-control techniques in a bid to prevent downpours during the opening and closing ceremonies of the Olympics.

Speaking in response to media questions on the safety of the methods, Zhang Qiang, director of the weather modification department of Beijing's meteorological bureau, said there is no scientific evidence of any harmful effects.

"Chemicals, such as silver iodide and liquid nitrogen, are widely used in rainfall suppression projects in many countries. And after years of research, meteorological experts from around the world have found no proof there is any negative impact on people's health or the environment," Zhang said.

"The amount of silver iodide that ends up in rainwater is very small, far below the national standard for drinking water," she said.

The other widely used chemical is liquid nitrogen, Zhang said, but as the atmosphere is itself about 78 percent nitrogen, this "poses no harm to the environment".

Based on weather records, meteorologists have said there is about a 47 percent chance of rain on Aug 8 in Beijing, the opening day of the Olympics. And while the world's scientists have yet to find a way to master Mother Nature, authorities hope their efforts will at least prevent a wash out on that particular day.

"If a rainfall reduction operation is conducted on a small scale, relatively good results can be expected," Zhang said.