Ammonia system safety, Part II

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Firefighters train to respond to an ammonia leak. Practicing for an incident before it occurs is a critical part of being prepared. (Photo courtesy of the Ammonia Safety Training Institute)

By Greg Scrivener

In the last issue, we discussed some basic safety information about ammonia as a refrigerant.  We are going to continue the conversation here by focussing on some elements of a proper safety and maintenance program.

Depending on the province, there are different requirements about what documentation and exact type of safety program you are legally required to have.  Regardless of the legal requirements, there are several safety program components that owners of ammonia refrigeration plants should want to have; the first is a good clear emergency response plan.

Developing a plan

There is always a possibility that a leak will occur and there is also always a remote possibility the leak is large and catastrophic. The exposure potential may be decreased by using lower charge systems, but it is not eliminated, and a game plan for how you are going to deal with these situations is paramount.

There are organizations like the Ammonia Safety Training Institute (ASTI) that have developed methods for emergency planning, or you can create your own.  In Canada, if your system has more than 4,500 kg of ammonia, you are required to register the system with Environment Canada and have what they call an E2 plan, which is a version of an emergency response/preparedness plan. At the end of the day you want your plan to clearly provide your organization with a plan that describes how you are going to address the following:

  • Prevention
  • Preparedness
  • Response
  • Recovery

We are going to skip discussing prevention for now and address it on its own in a future article.

Being prepared

Without adequate preparedness, it is impossible to have an organized emergency response.  Preparedness includes an understanding of what risks are present at your facility (usually this means doing a risk assessment) and what controls you are going to use to mitigate the risk potential or lower the magnitude of the event, the potential onsite and offsite consequences, the exact personnel who have a distinct role to play in the response.

Most importantly, being prepared means developing drills and internal training to make sure everyone understands the emergency response plan. This training and practice is often ignored, overlooked or, when it is done, underwhelming. Without practice, however, the emergency response plan will be useless in a real event.

In a practice I copied from a friend of mine, it is now my habit of to ask random workers in a facility what they would do if they smelled ammonia. The results of these interactions are not encouraging.

Doing a risk assessment means understanding what potential failure modes exist, thinking about the consequences of those failures, deciding what controls are present to prevent or minimize the failure and finally what response is required if the failure occurred.

There are several risk assessment methods available, each with their own advantages and disadvantages; a complete discussion of these methods here is not possible. Which ever way the risk assessment is done, it should leave you with a clear understanding of what you need to be prepared to deal with in an emergency. Following are some questions that lead to the development of your emergency response plan:

Fig. 1: This shows ammonia concentrations during an instantaneous release of 6,000 lbs. of refrigerant with levels of 35, 300 and 1,200 parts per million (ppm).

How much ammonia do you have?

This is critical in an emergency because you need to know what to tell the emergency responders. If you over estimate this number, they may evacuate an area much larger than needed. In a large facility with sophisticated reactions to leak events, you usually want to know how much ammonia can be isolated in specific areas so that you can be confident you have controlled the leak to a specific size.

What are the offsite consequences of a leak? 

There are some fairly easy ways to do dispersion analysis, but like all modelling programs, garbage in equals garbage out. Your emergency response plan should have well done dispersion analyses based on realistic leak scenarios.

Fig. 2: This is the same scenario, but the leak occurs over 10 minutes.

If you have a small plant or a low charge, you may want to include a scenario where all your ammonia leaks almost instantaneously; this may be realistic. For very large plants, there are very few failure scenarios that would cause an instantaneous or even very rapid release of the entire charge. If you decide to include a scenario like this in your emergency response plan (which you probably should), it must be absolutely clear that it is for extreme catastrophic failures.  Otherwise, you will find yourself evacuating a neighbourhood and closing highways for absolutely no reason.

This is why I think it is important to have several options available during a leak and be prepared to take different actions depending on the severity of the situation.

Fig. 3: In this incident, the same 6,000 lb. leak takes place over more than an hour.

Figures 1, 2 and 3  show a comparison between three scenarios, all of which involve a loss of 6,000 lb of ammonia. The highlighted areas represent the different concentration levels of 25 ppm, 300 ppm and 1200 ppm.

The difference between each scenario is the time that is takes to release the entire charge. In the first, it is released instantaneously, the second is over 10 minutes, and the third is over one hour.  It is immediately obvious that overrepresenting a possible leak scenario could have very significant implications in the emergency response. This is, of course, not to say that minimizing or underestimating a leak is appropriate either. This is why it is important to have accurate information available in an emergency.

What are you going to do about the leak?

Who is allowed to go into an area with elevated ammonia concentrations? Can your employees accompany the fire department or hazmat team? The fire department is not likely going to actuate or manipulate valves without very clear direction (often they will refuse regardless).  Does your contractor have the appropriate procedures to enter?

Again, there are several options and good and effective ways of dealing with this question, and the best time to figure this all out is in the comfort of a meeting room or office and not outside at night, in the freezing cold with news cameras pointed at your facility. You could easily end up losing the entire refrigerant charge and evacuating a large area because of a small leak that could have easily been contained.  It has happened several times before.

Who are you going to tell the reporters to phone?

Seriously. You may need to deal with this and having several people giving different information to different news agencies can be very unproductive and frustrating.

This is by no means a complete review of emergency preparedness, but it should give you a flavour of the thought and consideration that should go into planning. I hope this quick review also helped you gained an understanding of how valuable it is to have accurate information in an emergency.

I want to emphasize that while this whole process may sound intimidating, it does not have to be hard.  It takes some up-front work and some patience, but once you have integrated an emergency plan into your facility and practiced it thoroughly you will be a lot more comfortable if you have the misfortune of being involved in an incident.

Please note that this article is not intended to provide comprehensive safety advice and the author accepts no responsibility for any decisions made on the basis of the information provided.

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