Warning tonight for asthmatics from health boffins – don’t go and watch a fireworks display on a snowy night, apparently.

Who would have thought that such seemingly innocuous pastimes as muttering “Ooh, ahh” while building a snowman could have such potentially dangerous consequences?

Fireworks and snow can be a dangerous combination for asthma sufferers, researchers have found.

Barium, one of the metal salts used to produce spectacular bursts of colour from fireworks, is also known to constrict the airways.

Scientists in Austria found that after a firework display traces of the metal, which creates green effects, cling to snowflakes.

If the frosty particles were inhaled by asthmatics, it could aggravate their symptoms, the researchers believe.

Researcher Dr Georg Steinhauser and colleagues from Vienna University of Technology analysed fallen snow before and after a display in the Austrian village of Saalbach,

"We found huge amounts of barium in the snow", Dr Steinhauser told New Scientist www.newscientist.com magazine.

Concentrations were typically 500 times higher than they were in snow samples taken from the same sites before the display.

Fireworks have previously been linked to breathing difficulties in an Indian study.

During the Indian Diwali festival, a key part of which involves setting off firecrackers, the number of asthma cases rose by 12%. Some spectators without asthma had attacks of bronchitis.

Dr Steinhauser's team is now trying to develop fireworks that are free of barium and perchlorate, which provides the oxygen for pyrotechnic combustion.

Perchlorate can contaminate water supplies and is known to impair thyroid function and harm foetuses.