what's your budget? *********1-150 max
how noisy are we talking here? *******hearing protection mandatory loud, not like a rock concert maybe 1/3 to /1/2 that
http://en.wikipedia.org/wiki/Sound_pressure#Examples_of_sound_pressure_and_sound_pressure_levels
how close to the mp3 player/speakers would you be?******** "Within 3 ft"****
how portable does it need to be? could you provide some rough dimensions? ***"Overall speaker and player maybe something no bigger then 10*x6"x4" something roughly the size of a small radio"********
Do you mean the player has to come with an external speaker? or accept an external speaker? or have an internal speaker?++++++"would be willing to consider all of those options but it is handier to grab one thing and have it all"*********
how much does sound quality matter?********"its for work so won't go the pristine audiofle but nothing tinny sounding either perhaps something more midrange"*********
There are various battery powered speakers, though the sound quality, output volume, and battery life will be loosely related to size.
There are a lot of portable bluetooth speakers that are water/dust proof, but sound quality suffers at high volume. They should work reasonably well for you considering a noisy work environment isn't the best for noticing audio quality.