(6 km) front killing around 6,000 troops within ten minutes through asphyxiation. the gas being denser than air flowed downwards forcing troops to climb out of their trenches. reserve canadian troops, who were away from the attack, used urine-soaked cloths as primitive respirators. a canadian soldier realized that the ammonia in urine would react with the chlorine, neutralizing it, and that the water would dissolve the chlorine, allowing soldiers to breathe through the gas. 21st century china normally makes 10 million masks per day, about half of the world production. during the covid-19 pandemic, 2,500 factories were converted to produce 116 million daily. during the covid-19 pandemic, people in the united states, and in a lot of countries in the world, were urged to make their own cloth masks due to the widespread shortage of commercial masks.