So this actually happened to me recently (obviously). Flying about a ton of cargo. I had some freight loaded from the USPS that was leaking but in a bag we were not authorized to open and inspect (something about a felony to mess with US Mail). And right behind the flight deck. The bag smelled like actual ass juice so I figured a medical test sample (think quest diagnostics) had broken open (Rampers said it smelled like bad fish). So we offloaded the bag which was leaking pretty bad. The rampers "supposedly" inspected everything else. I close up (single pilot) smell still there. I go back to the rampers and had a talk with them. They swear up and down it's just residuals from the original offending bag. I'm on a timeline and got some pressure to go (get there itis real bad but didn't realize till later, no one ever does).
I take off and climbing through 1.5-2k the smell gets worse. I put on the O2 mask. I look to go back but due to the west coast being pretty much on fire the smoke has the approach below minimums. So going back wasn't an option. Only choice was to head elsewhere but the smoke made my destination the only option.
I get to altitude, smell is worse and leaking through the mask. I get on with center and request direct my destination and I am denied. Seattle is in flow control mode. I then request priority handling but clearly state I am "NOT" declaring an emergency, twice just to be sure it's understood. It's just a really bad smell, no emergency. But I gotta get out of this airplane. They give me direct to my destination. And let me keep warp factor 10 in all the way in.
I got asked for fire rescue standing by and declined again stating there is no emergency. Company comes up on company freq and tells me I need to have fire/rescue standing by just to check me out when I land. I let center know that company wants rescue waiting to check me out when I land. I am thinking they will meet me at the ramp and ask a few questions and that would be it. Maybe take a vital or two. (if shes cute maybe I get a date out of it).
NOOOOPEEE.....As I am coming in to land, they have the runway shut down, 5-6 heavies on both sides of the runway holding for me to land. Fire/rescue has everything rolled and waiting to follow me as I touch down. I touch down and taxi with 6 freaking rigs following me. I come to a stop near our area and they surround my aircraft. HAZMAT guys get out and come running towards me in full MOPP 4. I get out of my plane set the chocks and walk over to meet the guys in space suits. Explain the situation. They do their thing. And then come back and give the all clear.
Our DG guys then off load all the stuff, find two boxes the mail bag had leaked on and put the rest on the trunk aircraft. By then most of the liquid has dried and the smell mostly dissipated but people can definitely smell it in the airplane. But it isn't anywhere near as bad as it was upstairs.
Not a word was said to me but I feel pretty ridiculous for all the attention and overreaction. Wasn't in any way an emergency though I didn't know what the smell was. I was pretty sure it wasn't anything dangerous. Just wanted to get some different viewpoints on my decision making. I am second guessing myself.