surveillance footage from philadelphia 's 15th street station shows one passenger lose his balance as he tries to skirt past somebody on the platform at 6.40 on wednesday night .
he was walking close to the edge of philadelphia 's 15 street station platform on wednesday at 6.40 pm when he tumbled .
his would-be rescuer is seen walking along the platform -lrb- center -rrb- , initially unaware that the platform is one of many slated to be renovated and modernized in a four-year development project starting next year .