The Soldier at the Western Front – The Use of Flamethrower
Source 1: Louis Barthas: Poilu

Louis Barthas, cooper by profession, was drafted in the age of 35 to serve in the French army in August 1914. He served in the rank of NCO in an infantry regiment and described in his memories his personal experiences at the front, among others in the trench warfare at Verdun. His book was published posthumous in 1978 and was one of the first published diaries and collections of letters concerning the First World War.
In the following excerpt Barthas reports about an attack of the German army on the 6th June 1915 in the Second Battle of Artois, a battle with severe loses in northern France.

”But what is this? Has Hell opened up under our feet? Are we right at the rim of a furious volcano? The trench is filled with flames, with sparks, with bitter smoke, the air is unbreathable. I hear hissing, crackling, and alas, yes, the cries of pain. [...] At my feet two miserable creatures are rolling on the ground, their clothes, their hands, their faces on fire – blankets, tent cloths, sandbags. The Germans had just fired some sort of incendiary liquid on us.”

Louis Barthas: Poilu. The World War I Notebooks of Corporal Louis Barthas, Barrelmaker, 1914 – 1918, New Haven 2014, p. 80.