burning metal (possibly even serving as an additional oxidizing agent). Since these reactions are well understood, it has been possible to create specific water-additives which will allow: A better heat absorption with a higher density than water. Carrying free radical catchers on the fire. Carrying foaming agents to enable water to stay on the surface of a liquid fire and prevent gas release. Carrying specific reactives which will react and change the nature of the burning material. Water-additives are generally designed to be effective on several categories of fires (class A + class B or even class A + class B + class F), meaning a better global performance and usability of a single extinguisher on many different types of fires (or fires that involve several different classes of materials). Multi-scale fire triangles for wildland fires In the context of wildland fire, the fire triangle can be scaled up to apply to fire spread over landscapes (scales of days and several kilometres) and recurrence of fire over time (scales of decades and hundreds of kilometres). Thus, while heat is important to ignite a flame, topography is important for aiding fire spread especially by preheating upslope fuels, and ignitions sources are important to help explain recurrence on longer time scales. Similarly, while oxygen is relevant to sustain a flame, weather and associated winds feed oxygen into a spreading fire, and the longer-term pattern of weather is summarized as climate. Lastly, fuels is the term to describe what burns in a single flame to the range of materials burnt in a spreading wildfire, but fuels vary over larger space and time scales in what is called vegetation. At the smallest scale, the combustion fire triangle, individual fuel particles are ignited once at a critical temperature, and fire transfers energy to the nearest surroundings. Combustion events range on the scale of several seconds to a couple of days and their effects are monitored at the quadrant scale. The largest scale, in contrast, describes the fire regime concept. Global climate change drives many of the factors involved in the 'wildfire' and the 'fire regime' triangles. For example, with respect to the fire regime, a particular vegetation type will support a characteristic fire in terms of recurrence, intensity, seasonality and biological effects; a change in vegetation type will have implications for a changing fire regime. See also Glossary of firefighting terms Fire classes Notes References