So much human excrement was drawn into one San Francisco subway escalator that a HAZMAT team was required after it ground to a poo-glued halt. Will Kane in SFGate:
While the sheer volume of human waste was surprising, its presence was not. Once the stations close, the bottom of BART station stairwells in downtown San Francisco are often a prime location for homeless people to camp for the night or find a private place to relieve themselves. All those biological excretions can gum up the wheels and gears of BART's escalators, shutting them down for long periods of extended repairs, increasing station cleaning costs and creating an unpleasant aroma for morning commuters.
