Smoke is a strange mixture of exotic pollutants and incomplete combustion products. Of course, some people smoke cigarettes for the pleasure of it.

For most people smoke is unpleasant and should be avoided. Many people watch firework displays and go "wow" and the smoke from them adds a bit of the zest to the event.

The metallic particles in the smoke emitted by fireworks pose a health risk, particularly to people who suffer from asthma. This is the conclusion of a study led by researchers from the Institute of Environmental Assessment and Water Research, published this week in the Journal of Hazardous Materials. Smoke is a colloid and comprises a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass.

The composition of smoke depends on the nature of the burning fuel and the conditions of combustion. Fires with high availability of oxygen burn at high temperature and with small amount of smoke produced; the particles are mostly composed of ash or complex aerosols. Carbon and hydrogen are almost completely oxidized to carbon dioxide and water. Fires burning with a lack of oxygen produce a significantly wider palette of compounds, many of them toxic.

"The toxicological research has shown that many of the metallic particles in the smoke from fireworks are bio-reactive and can affect human health", states Teresa Moreno, a researcher from the Institute and lead author of a study that has been published this week in the Journal of Hazardous Materials.

The different colors and effects produced in these displays are often achieved by adding metals to the gunpowder. When a pyrotechnic display takes place it releases a lot of smoke, liberating minute metallic particles (of a few microns in size, or even less), which are small enough to be inhaled deeply into the lungs.

The study focused on the San Juan fiestas (the night of 23 June through to 24 June, 2008) in the Spanish city of Girona. The researchers analyzed the levels of more than 30 chemical elements and compounds in May and June in order to confirm that the levels of lead, copper, strontium, potassium and magnesium skyrocketed after the fireworks were launched.

The team found the results were similar in other towns too. During the Mascletà (18 March), for example, in the Las Fallas fiestas in Valencia, levels of these elements rose once again, as well as others such as aluminum, titanium, barium and antimony, and also concentrations of nitric oxide (NO) and sulfur dioxide (SO2).

The researcher compares the problem with that of tobacco. "The less you expose yourself to the smoke, the fewer negative effects it will have on your health, and so the best solution is to avoid inhaling it".

According to the scientists, in the absence of a ban on fireworks (and remember people like fireworks and as a result do not consider it risky), spectators should stay well back in a place not affected by the smoke and pay attention to the wind direction. They also recommend that fireworks displays should be sited in a place that ensures the plume of smoke will blow away from densely populated areas.

It is not known how much of an increased risk such exposure to firework smoke may be. Obviously those with asthma or similar should avoid not only firework displays but many other activities.