1. For the purpose of classifying a substance or preparation dangerous for supply or carriage in accordance with Part I of this Schedule or Part I of Schedule 3, the flash point shall be determined—
(a)by one of the equilibrium methods referred to in paragraph 3; or
(b)by one of the non-equilibrium methods referred to in paragraph 4, except that when the flash point so determined falls within one of the following ranges, namely:—
(i)−2°C to + 2°C,
(ii)19°C to 23°C, or
(iii)53°C to 57°C,
that flash point shall be confirmed by one of the equilibrium methods referred to in paragraph 3 using like apparatus.