A method of testing a battery comprising: setting up the battery in a test environment; puncturing or heating the battery in the test environment to cause the battery to produce a fire having a flame that extends out from the battery; capturing a digital video including a series of digital images of a scene that includes at least a portion of the test environment and the flame that extends out from the battery, the digital images being captured using a digital camera that forms the digital images using visible light where the digital camera is positioned external to the test environment; the method characterised by uploading the series of digital images of the scene to a computer configured to determine dimensions of the flame in the scene based thereon, including the computer being configured to at least: produce a quiver plot of the scene from the digital images, the quiver plot including a plurality of velocity vectors that represent motion of gases in the scene, the motion of gases including motion of gases in and around the flame, the plurality of velocity vectors originating at a respective plurality of points in the quiver plot and having respective magnitudes and directions; identify a point of the respective plurality of points as an origin point to represent an origin of the flame in the scene; select or receive selection of other points of the respective plurality of points based on similarity of at least the directions of the velocity vectors originating at the origin point and the other points, the origin point and the other points defining a polygon in the quiver plot that is an approximate outline of the flame; determine dimensions of the polygon in the quiver plot; translate the dimensions of the polygon in the quiver plot to corresponding dimensions of a polygon in the digital image; translate the corresponding dimensions of the polygon in the digital image to dimensions of the flame in the scene; and generate a displayable report that includes at least the dimensions of the flame. setting up the battery in a test environment; puncturing or heating the battery in the test environment to cause the battery to produce a fire having a flame that extends out from the battery; capturing a digital video including a series of digital images of a scene that includes at least a portion of the test environment and the flame that extends out from the battery, the digital images being captured using a digital camera that forms the digital images using visible light where the digital camera is positioned external to the test environment; the method characterised by uploading the series of digital images of the scene to a computer configured to determine dimensions of the flame in the scene based thereon, including the computer being configured to at least: produce a quiver plot of the scene from the digital images, the quiver plot including a plurality of velocity vectors that represent motion of gases in the scene, the motion of gases including motion of gases in and around the flame, the plurality of velocity vectors originating at a respective plurality of points in the quiver plot and having respective magnitudes and directions; identify a point of the respective plurality of points as an origin point to represent an origin of the flame in the scene; select or receive selection of other points of the respective plurality of points based on similarity of at least the directions of the velocity vectors originating at the origin point and the other points, the origin point and the other points defining a polygon in the quiver plot that is an approximate outline of the flame; determine dimensions of the polygon in the quiver plot; translate the dimensions of the polygon in the quiver plot to corresponding dimensions of a polygon in the digital image; translate the corresponding dimensions of the polygon in the digital image to dimensions of the flame in the scene; and generate a displayable report that includes at least the dimensions of the flame. produce a quiver plot of the scene from the digital images, the quiver plot including a plurality of velocity vectors that represent motion of gases in the scene, the motion of gases including motion of gases in and around the flame, the plurality of velocity vectors originating at a respective plurality of points in the quiver plot and having respective magnitudes and directions; identify a point of the respective plurality of points as an origin point to represent an origin of the flame in the scene; select or receive selection of other points of the respective plurality of points based on similarity of at least the directions of the velocity vectors originating at the origin point and the other points, the origin point and the other points defining a polygon in the quiver plot that is an approximate outline of the flame; determine dimensions of the polygon in the quiver plot; translate the dimensions of the polygon in the quiver plot to corresponding dimensions of a polygon in the digital image; translate the corresponding dimensions of the polygon in the digital image to dimensions of the flame in the scene; and generate a displayable report that includes at least the dimensions of the flame.