Think of it this way: what do others need to tell you before you let them into your house to perform an activity you have no clue about? Surely it helps if they tell you it's for a non-profit project that helps someone in need / solves a problem / makes the world a better place? Or if they do something that might benefit you, or that is linked to something you like? And you'll probably ask them to go away if they state their intention is making money with the stuff they gather at your place, without compensating you, right?

I think affiliation does play a role, but a convincing talk tailored to that specific recipient might be even more important.

You have to get people interested in what you are doing. You'd be surprised what and where you get to when people are enthused. The personal touch always works best, find out who really has the say, and network, you probably have some connection already, see if you can get an introduction, either from head office or someone who already works there.

The main thing is to be polite and persistent, but also accept that no, means no.

EMV and Iain says it very well, but to add my own view to that: I've been to several downright hazardous places, and it has always without exception ended up that way because I've earned their trust and proved my reliability by NEVER EVER making demands or bitching about anything, but happily accepting any position I might be given, no matter how bad it might really be. If I end up getting anything I'm happy, if not, cest la vie, I tried :-) But the first thing I always do is clarify that I'll leave in an instant if they find me even in the least bit annoying. I also make perfectly clear how far I am willing to go myself, stating I'm not a daredevil, and some of these places actually square scares me into sometimes ridiculous carefulness and respect. A dock or train-yard might not seem very threatening, but there are much really heavy machinery, and even the smallest moment of inattention from someone not used to the place might end up badly. The foremen knows this.

When I visit locations there are never no guarantees I'll get any better position after being granted a position, and they might very well say no to even being in the vicinity of the place, but mostly when they'll come to trust me I got very nice things, sometimes even surprising me beyond what I could ever imagine! My greatest pride, that I can actually talk about, was a humongous display-window in a former mall that was up for razing. The foreman didn't wanna let med smash it at first because it would let the dust spread, and quite frankly we both knew what would happen if I cut myself at their location. After being allowed closer and closer as time passed 'till getting some truly amazing positions to the razing, wearing their protective gear, he actually ended up happily smashing it for me and boarding up the gaping hole with plywood! :-)

Mind you, most people actually think these kind'a things are fun, but are not willing to take the consequences if anythings goes wrong and/or anyone would get injured or killed. We must respect that, and neither should we.

One option is the 'official' angle, and one way that may be achieved is by finding out if your city has a Film Locations office, many do. They are often affiliated to City Councils and their function is to help make shooting films in the city possible & efficient. When I wanted to record Fireworks I contacted the local film office and they helped me get fire permits and safety advice, and suggested locations for me. Once I'd narrowed down to a few locations they helped me get permission, and advised me on what I needed to do eg I had to drop letters in the mailboxes of anyone in the immediate area, explaining what we were doing and when. The cost varies from nothing to lots, depending on what potential disruption you create, but I was very impressed with the local Film office - they were very approachable and super helpful.