Sunlight As An Ignition Source

Michael Rushton
Office of the Ontario Fire Marshal, Canada

Presented at the International Symposium on Fire Investigation Science and Technology, 2018


The common methodology and approach to fire investigation is to determine an origin and then inventory potential ignition sources within that origin. One potential shortcoming of this approach is if the ignition source cannot be found or does not originate from within the fire origin area. One of such possible elusive ignition source could be related to solar radiation, which originates from the sun in the form of visible and invisible light.

This paper approaches the subject of the propensity of ignition of common combustible materials as a result of exposure to a concentration of radiation originating from the sun. The paper explores various test set-ups, designed to focus sunlight through the means of refraction and reflection in order to concentrate sunlight across a specific two-dimensional target surface ultimately resulting in significantly larger radiant heat fluxes than the surrounding environment.

A total of 282 tests were conducted with various setups, which allowed for sunlight radiation to be focused onto ignitable materials such as paper. Many of the tests resulted in successful ignition of the materials. To quantify the observations, a heat flux sensor was used to measure the power produced by these various setups.

Lastly, the factors and parameters that would be required for this kind of ignition scenario(s?) are discussed. Based on the empirical data collected in the experiments, a formula is derived to represent some of the variables and also to approximate the heat flux output which can be expected from an optic object or focusing device such as a magnifying glass.


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