In the 1940s, Philadelphia churned out ships, bombs, and a menagery of items for their troops over in Germany and France. Unfortunately, they did not possess the Chemical safety knowledge we have now. Many industrial and chemical plants were built inside Center City.
Now what if something like Bhopal or Baia Mare occurred in Philadelphia at the time?
What would be the impacts on Americans fighting in World War Two?
Industrial, yes: but we're talking about such things as Disston (saws) and the granddaddy of them all, Baldwin Locomotive on Spring Garden Street (before moving to Essington). But chemical? Not really. Philadelphia's chemical/refining industrial locations are either in the northeast (the one-time Allied/now Sunoco Chemical near I-95) or south Philadelphia (the Sunoco refinery on Passyunk at Pt. Breeze; the Atlantic/Arco/Gulf/Sunoco refinery immediately adjacent).
Hard to imagine an accident at Baldwin causing a major disruption unless it happened to be a multi-alarm fire. And a refinery upset...well, again likely we're talking a fire that might well disrupt northeast corridor rail traffic at a very inopportune time, rather than a Bhopal-like incident.
Now, if it's something like that you want, I refer you instead to du Pont's Chambers Works at Deepwater, NJ (in the shadow of the present-day Delaware Memorial Bridge). In those days, du Pont was engaged in (among other things) the first industrial scale production of elemental fluorine, which was essential to production of uranium hexafluoride for the Manhattan Project. You want trouble? A massive release of fluorine gas would be devastating between its poisonous qualities and the fires induced by its virulent reactivity. And when such gas passed over water--namely, the neighboring Delaware River--you'll get clouds of pernicious hydrogen fluoride gas, which, in a mist form, can carry for miles. Philadelphia may not get in trouble, but depending upon prevailing winds, Wilmington, DE very well might.