Friday, August 23, 2013

Chemical Safety and Security EO – Reactive Chemical Hazards

This is part of a continuing series of blog posts discussing President Obama’s recently signed executive order on “Improving Chemical Facility Safety and Security” (EO 13650). The other posts in the series are:

Section 6(c) of the EO requires the EPA and OSHA to look at adding ‘additional regulated substances and types of hazards’ to their respective chemical safety programs. First and foremost (this is a response to the West Fertilizer incident after all) would be adding ammonium nitrate to the list of covered chemicals. Additionally, the Chemical Safety Board has long advocated the addition of ‘reactive chemical hazards’ to the coverage of these programs. In this post I’ll look at some of the types of hazards that this might include.

Reactive Chemical Hazards

There are a huge variety of known and potential chemical reactions. Under the wrong circumstances any one of these reactions could be considered hazardous, either in the products consumed or produced or the energies consumed or produced. No one advocates expanding the either the RMP or PSM programs to cover all of these reactions. Only those reactions that are sufficiently dangerous in their consequences that they pose an imminent danger to life, limb or property should be considered.

As a general rule the EPA Risk Management Plan (RMP) program would be best suited to the management of chemical processes that would have significant off-site consequences if the reactions got out of control. The OSHA Process Safety Management (PSM) program would address those that would potentially affect the health and safety of on-site personnel if they were not properly controlled. Since it is hard to imagine a process that could have significant off-site consequences without affecting facility personnel, it seems obvious that the PSM program should cover more chemical reactions than the RMP program.

I’ll leave for a separate discussion whether or not these reactions (or some sub-set of the reactions) should be considered for coverage under the CFATS program.

Defining the Reactions

One of the reasons that both EPA and OSHA have been dragging their feet on implementing the CSB recommendation to include reactive chemical hazards in the RMP and PSM safety programs is the difficulty in defining exactly what chemical processes or reactions would be covered. Both programs currently rely on a printed list of chemicals to determine what is covered and what isn’t. Things won’t be that easy with reactive chemical hazards.

To see why let’s look at a common class of reactive chemicals, monomers, and look at how we might determine which ones would be regulated and which wouldn’t. First, monomers are molecules that react with similar molecules to form long chains called polymers. Polymers can be made out of chains of one type monomer or multiple types.

Most polymerization reactions produce heat as a byproduct of the reaction. With most reactions the higher the temperature the reaction takes place at, the faster the reaction takes place. Thus, normally the heat of polymerization increases the rate of polymerization. For all practical purposes the polymerization reaction continues until all of the available monomer is consumed in the reaction.

In a commercial polymerization process the ratio of reactants and solvents, initiators (chemicals that start the polymerization process) and inhibitors (chemicals that impede the polymerization process) and reaction conditions of temperature and pressure are all tightly controlled to produce a specific desired polymer.

Polymerization Hazard

In an improperly controlled process a number of things can go wrong to make bad things happen. Most of those ‘bad’ things are bad in the business sense; off-spec material is produced that must undergo additional handling and possibly costly disposal. Those consequences are of no real concern to the PSM or RMP programs.

In some cases, however, dangerous bad things can happen. For example, when polymerization takes place in a volatile solvent the improperly controlled heat of reaction can heat the solvent to the boiling point greatly increasing the pressure in the reaction vessel. If that vessel is not properly vented, the pressure can increase to the point where the vessel catastrophically fails in an incident that closely resembles an explosion. If the solvent is above its flashpoint and there is an ignition source available near the vessel failure there may be a fire or even an actual explosion that results. That type of reaction could certainly be of concern to an EPA or OSHA regulator.

The regulatory definition problem here is that it is the combination of the monomer and solvent that is dangerous. With a different solvent, no solvent, or more solvent there might be no way the reaction could produce enough heat to reach the boiling point. If the boiling point cannot be reached there is nothing of interest for the EPA or OSHA to regulate.

Now, you could define a regulatable (made-up word) polymerization process as any combination of solvent and monomer in a single container that the heat of polymerization of the available monomer is sufficient to raise the available solvent to its boiling point. Those are values that can be reasonably calculated from publicly available data for most monomers and solvents. Where the information is not publicly available any competent chemist or chemical engineer or laboratory technician can measure the appropriate data in a reasonably equipped laboratory.

Other Reactions

A polymerization reaction is the easiest of the potentially dangerous chemical reactions to define and it is probably one of the least violent. To be really dangerous on a catastrophic scale you have to turn to reactions that not only produce heat but also evolve gasses. A good example of this type of reaction is the self-accelerating decomposition reaction (SADR). These reactions typically involve chemical intermediates and are much more difficult to describe in a concise manner. To see a good discussion of the hazards involved in this type of reaction see the Chemical Safety Board’s investigation of the T2 Laboratories explosion.

Establishing a regulatory definition for these types of reactions will be much more difficult. Relying on a list of reactions will be of very little use. People using known SADR reactions will typically be taking appropriate precautions. The newly discovered reactions of this type are most often described in accident literature.

Expected Working Group Actions

I will be very surprised if the Working Group is able to do much more by the November 5th deadline for the §6(c) requirement to look at reactive chemistries than recommend that ammonium nitrate be added to the current list PSM and RMP chemicals. Actions beyond that will be rely on reaction descriptions that will be too controversial to be able to resolve through just a standard rule making process. They will require legislative action on a complex technical issue that there is currently no political consensus to support.

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