I work at Intel at one of their major fabs in the Arizona desert.
Our emergency procedures are virtually identical to Amazon's, and our corporate health services explains why: Our facility is huge (the campus is probably a square mile in size, and the buildings are around 100,000 to 200,000 ft^2 each), and the nearest fire station or ambulance station is about a mile away. As a result it will take the local paramedics a long time to arrive and render aid. It is much faster to call our internal emergency response team (ERT) -- they will dispatch ERT parametics to render first aid and call 911 as necessary, and will direct local paramedics. Our ERT routinely trains how to get to any point on the campus within a couple minutes; our ERT is also composed of ordinary people doing non-ERT jobs throughout the campus, who are trained to respond to an ERT callout at a moment's notice.
A few years ago we had a worker literally drop dead somewhere in our fab; it was never released exactly what killed him, but they ruled it was not an industrial accident (likely a heart attack or heat stroke). What they learned from the investigation is that this individual wandered off to do something without telling anybody, and no one knew he was missing until he had already died. If you know anything about large factories, you know how easy it can be to disappear and no one notice you missing; this is exactly what happened in this case. Its why, for your own personal safety, you should always make sure someone knows where you are at all times, and have a means of contact you and you to contact others for help (whether its two-way radio, cell phone, or some other means).
As much flack as Amazon gets and often deserves, this is not one of those times they deserve it.