No one was injured when an explosion and fire ripped through part of the sprawling Sunoco plan in Marcus Hook back in May.

Until yesterday.

Now we know the true cost of the blaze. It will cost 50 people their jobs.

Sunoco yesterday announced it would not rebuild the ethylene unit where the blast rocked the area back on May 17. They say the demand for ethylene products does not justify the money they would have to put into the project.

They notified 40 to 50 union workers that the closure would cost them their jobs. Exactly who will be laid off has not yet been determined. It likely will go according to seniority at the plant.

It’s another downturn for Sunoco as they try to deal with the souring economy, which has put a dent in those huge profits that were rolling into the company.

The firm went through very contentious labor negotiations with the unions that represent workers at their Philly and Marcus Hook refineries.

They were unsuccessful in achieving the layoffs and savings they were looking for from their unioni workers. So they turned their sights elsewhere.

A couple of weeks later, the firm announced it would lay off 750 salaried workers, most of them at their downtown headquarters.

The move was criticized by Gov. Ed Rendell, who blasted the company’s decision to enact such steep layoffs when they had posted huge profits just the year before.

But Sunoco made it clear that the economy had since gone south, and their business was affected the same as everyone else.

That meant in order to remain competitive and offer return for their investors, they needed to make cuts.

It’s the same thought process that looked at the demand for ethylene products, compared it to the cost involved in rebuilding the damaged unit at the Hook plant, and decided the prudent thing to do would simply be to shutter the facility.

That explosion back in May was heard and felt all over lower Delaware County.

Yesterday’s announcement didn’t make a sound. But the message came through loud and clear.