“All I know is what I read in the papers.”  — Will Rogers

When there is a catastrophic release of highly hazardous chemicals, I want to know about it. I want to know what happened, why it happened, and what I can learn to keep it from happening again.

I go to news accounts. All too often, though, the accounts are clearly wrong.

That doesn’t mean that there is nothing to learn from newspaper accounts. It just means that it will take a lot of sifting and sorting to understand what is true, and what is idle speculation by a reporter whose job it is to sell newspapers.

Explosion at Watson Grinding and Manufacturing

On Friday, January 24, 2020, at 4:24 am, there was an explosion at Watson Grinding and Manufacturing in Houston. Watson employs over 100 workers; the explosion killed two employees. Additionally, 20 nearby residents were injured. Authorities quickly dismissed arson or terrorism as the cause; press accounts suggest that their attention was on a 2000-gallon propylene storage vessel, with leaking propylene the cause of the explosion

Watson Grinding and Manufacturing is not a chemical manufacturer. Instead, it manufactures and services large parts, specializing in hard metal alloys. Propylene is not a raw material at the facility, but a fuel with highly desirable combustion characteristics.

A History with OSHA

When there is an incident resulting in fatalities, most news organization feel compelled to check to see if there is a “record”. For workplaces, the record of interest is a history of OSHA citations.  Several news accounts reported that Watson was inspected by OSHA and fined in 2013 for failing to control hazardous energy and for electrical safety violations. The fine was around $8,000.

For those who don’t know, failing to control hazardous energy is a reference to the Lockout-Tagout standard. That means that employees worked on equipment with the guards removed and were not adequately protected against that equipment’s accidental start-up. Electrical safety citations cover a wide range of violations, from using extension cords as a substitute for permanent wiring to improperly ground electrical equipment, from failing to label electrical disconnects to using electrical rooms as storage closets.

In 2013, the maximum fine for a first-time OSHA violation was $7,000 per citation and the minimum fine was $350 per citation. That Watson was cited for at least two violations and received a total fine of $8,000 means that OSHA did not hit them as hard as they could have.  A slap on the wrist? Perhaps. Or perhaps OSHA simply determined that the violations were not egregious but did not want Watson to believe that the violations were acceptable.

In any case, OSHA returned for a follow-up inspection in 2015 and did not cite Watson for any further violations.

A Failure to Disclose?

One news account made much of the fact that propylene is covered under the EPA’s RMP Rule (40 CFR 68) and as a flammable gas, under OSHA’s PSM Standard (29 CFR 1910.119). Both regulations, as well as others, cover processes where there is more than the threshold quantity of 10,000 pounds. For these standards, the term “process” includes storage. OSHA’s PSM Standard requires compliance but no reporting to OSHA. The EPA’s RMP Rule, on the other hand, requires submission of a Risk Management Plan for covered processes.

Did Watson have over 10,000 pounds of propylene in their process?

If the only storage was the 2000-gallon storage vessel, then no. At standard conditions—70°F and atmospheric pressure—the density of propylene gas is 0.1105 lb/ft3. If the storage vessel contained gas at standard conditions, it could only hold 29½ pounds. But no one would install a 2000-gallon storage vessel to hold 29½ pounds. When propylene is compressed to 137.5 psig at 70°F, it becomes liquid, with a density of 31.92 lb/ft3. At that density, a 2000-gallon storage vessel will hold 8,535 pounds of propylene, assuming that the vessel is absolutely full.

Clearly, Watson did not have over 10,000 pounds of propylene in their process.

They did not fail to disclose. They simply were not required to. The agencies picked the threshold quantity, not Watson. Some amount must be small enough that the regulations do not apply. The line has to be drawn somewhere. Right now, the line is at 10,000 pounds, and Watson wasn’t even close to the line.

And Yet…

And yet, 450 structures were damaged, including 35 with major damage. Twenty residents were injured. Worst of all, Frank Flores and Gerado Carasquillo died in the explosion.

The general duty clause of the Occupational Safety and Health Act requires all employers to provide a workplace free from recognized hazards that can cause death or serious injury.  There can be no question that the flammability and explosivity of leaking propylene is a recognized hazard.

Propylene has a heat of combustion of 48,500 kJ/kg. Using the 10% yield stipulated by the EPA for worst case scenarios, that means that pound-for-pound, liquefied propylene has about the same explosive energy as TNT.  In this case, a little over 4 tons.

Yes, a 2000-gallon vessel storing propylene is clearly a recognized hazard.

Then Why Take the Press to Task?

As far as I can tell, the press did not get any facts wrong. The fault is in the context, or lack of context. Still, people died and Watson did fail to control a serious hazard. So, why take the press to task?

Why? Because it is important that we focus our efforts on what matters. Working on the wrong things doesn’t make workplaces safer.  Worse, because resources are finite, working on the wrong things means that we aren’t working on the right things.

Attempts to paint Watson Grinding and Manufacturing as villainous on account of irrelevant OSHA citations makes for a tidy picture, but it doesn’t help. Watson used a fuel. The very characteristics that made it a desirable fuel also made it a flammability and explosivity hazard. Watson is not the only company that uses fuels.  In fact, we all do. Calling propylene a “hazardous chemical” makes it too easy for others to look past their own hazards.  After all, Watson was not operating a chemical plant. It was operating a manufacturing plant that made parts. It was doing the kind of work we are keen to bring back to the U.S.

Look at Your Own Hazards

Process Safety Management is a regulation. Managing process safety, on the other hand, is a way of dealing with process hazards that can result in fires, explosions, or toxic releases. Leaking fuels are a hazard. So is the loss of containment of anything that can burn or result in a toxic exposure. Whether or not a facility is covered under the standards or is a “chemical company”, they need to apply the principles of process safety to their operations.  It’s the only way to live.


  • Mike Schmidt

    With a career in the CPI that began in 1977 with Union Carbide, Mike was profoundly impacted by the 1984 tragedy in Bhopal and has been working on process safety ever since.