Shrapnel and bullets are "clean". Phosgene, chlorine, mustard and the rest would rot your lungs and blister your skin.

       Bent double, like old beggars under sacks,
       Knock-kneed, coughing like hags, we cursed through sludge,
       Till on the haunting flares we turned our backs
       And towards our distant rest began to trudge.
       Men marched asleep. Many had lost their boots
       But limped on, blood-shod. All went lame; all blind;
       Drunk with fatigue; deaf even to the hoots
       Of tired, outstripped Five-Nines that dropped behind.

       Gas! Gas! Quick, boys! – An ecstasy of fumbling,
       Fitting the clumsy helmets just in time;
       But someone still was yelling out and stumbling,
       And flound'ring like a man in fire or lime . . .
       Dim, through the misty panes and thick green light,
       As under a green sea, I saw him drowning.
       In all my dreams, before my helpless sight,
       He plunges at me, guttering, choking, drowning.

       If in some smothering dreams you too could pace
       Behind the wagon that we flung him in,
       And watch the white eyes writhing in his face,
       His hanging face, like a devil's sick of sin;
       If you could hear, at every jolt, the blood
       Come gargling from the froth-corrupted lungs,
       Obscene as cancer, bitter as the cud
       Of vile, incurable sores on innocent tongues,
       My friend, you would not tell with such high zest
       To children ardent for some desperate glory,
       The old Lie; Dulce et Decorum est
       Pro patria mori.

                                 --Wilfred Owen