Lots of whom were spectators that were drawn to watch the efforts to control the overheating ammonium nitrate before it blew.
I worked at the site of this explosion for 5 years (1988-1992). Entering the front gate, I used to walk past a large memorial that had the 500+ names. Never once did I pass it without thinking about the importance of being safe in what I was doing.
In my first year there, our neighbor, Marathon refinery, had a fire. It was raining at the time, so... I grabbed my raincoat and headed out to take a look. As I walked through the control room, I passed one of our most senior operators, who... while tweaking a valve setting ask, "Where ya headed?".
I replied, "I heard Marathon has some kind of fire. Thought I'd go take a look".
Without looking away from what he was doing he responded, "Suit yourself... Course ya know, most of those people who died back in '47 were 'just looking'".
I paused, turned around, and said... "On second thought, I think I have some work in my office".
He dryly responded, "Suit yourself".