Trains transporting toxic or explosive products travel through populated areas frequently. Like all consists (refers to the makeup of the entire train), various financial considerations influence where and for how long such trains remain stopped in stations and trainyards across the continent. I believe that more attention needs to be paid to the risks to populations who live adjacent to the railway tracks.
The air brakes on train cars are set and released by events in the pressurised lines that run the length of the train. There are manual brakes on each car that can be set to assure the train will not move even if the air brakes malfunction. Setting the manual brakes requires more human labour and are thus more expensive to the company. Company policies usually dictate how many manual brakes will be set. Government regulations may specify what should be done but the profit motive and the adequacy of government inspection ultimately determine what is done.