The blast happened about 20 minutes after the first report of a fire at the fertilizer facility.

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Assistant State Fire Marshal Kelly Kistner told CNN that 18 Texas firefighters have died on duty so far this year, including 10 first responders killed in an explosion at a fertilizer distribution facility in West, Texas.

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Ms. Monforton said she didn't think the West Fertilizer Co. facility that exploded Wednesday night in West, Texas, was "going to be on OSHA's radar screen" because it apparently had few employees, despite the fact that it stored highly combustible anhydrous ammonia.

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Zak Covar, executive director of the environmental-quality commission, said the fertilizer storage and blending facility had existed since 1962, before permits were required, and was allowed to remain on the site.

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San Francisco currently has a large compost facility that turns food waste into fertilizer.

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Sanergy employees empty the toilets each day, taking an air-tight container of waste to a Sanergy processing facility where it is converted to biogas and fertilizer that Sanergy plans to sell to commercial and small farmers.

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