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Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

Posted May 08, 2013 1:51 PM by jsavage

The recent incident in Texas has prompted us to think about understanding the risks associated with operating a facility handling hazardous materials, and how to prevent these types of incidents. (Current estimates reveal that the facility contained as much as 54,000 pounds of toxic anhydrous ammonia, and reported to the Texas State Health Services Department that it possessed 270 tons of ammonium nitrate.)[1]

Since the explosion has also likely made many manufacturers re-evaluate their own facilities, we thought providing a starting point for this evaluation would be helpful. A quantitative risk analysis (QRA) is a good starting point because it attempts to quantify risk from potential incident scenarios so that you can focus on those with the highest risk. It does this by evaluating the consequence of a particular event vs. the probability of that event occurring, to determine the overall level of risk. This type of evaluation is key for low probability, but high consequence events. A QRA allows a company to identify high risk scenarios, and allocate resources towards preventing these.

QRA Steps

  1. To perform a QRA, a team must first identify the hazards that exist through a Process Hazard Analysis, which may include a HAZOP review. The regulation, OSHA 3133, Process Safety Management Guidelines for Compliance, provides an explanation of the methods for this analysis.
  2. Then identify the consequences that result if the hazards are released upon the plant or the surrounding community. There are a number of tools readily available to conduct consequence analysis, such as PHAST.
  3. Once a consequence has been established, the second key part of the QRA is needed: determining the probability of an event. This probability can be determined through various methods, such as fault tree analysis, or layer of protection (LOPA) analysis. Executing a fault tree analysis can be prohibitively expensive, and the results depend on the team recognizing all of the failure modes of complicated systems. For this reason, many organizations are using LOPA to estimate the consequences of a loss of containment of a hazardous material.
  4. A company can then analyze its risk based on the position of various events on a consequence vs. probability plot, which describes the exposed risk. The organization can then make the determination whether the risk of a particular event is too great based on a number of factors, and implement changes or improvements to bring that risk in line with the organization's goals.

Like any method for estimating probabilities, the limitations of the QRA include such factors as predicting human behavior during stressful conditions (although one can apply a factor for this.) The reliability of any safeguards is also important to consider. This is highly dependent on the safety culture of an organization, because maintenance and testing of safeguards is a key part of making sure these work when called upon.

Organizations such as the Center for Chemical Process Safety (CCPS at www.aiche.org) provide a wealth of reference materials and training courses that can help an organization determine how best to perform a QRA and implement the changes needed to mitigate the risk associated with a facility, specific operating unit, or a process.



[1] http://news.yahoo.com/texas-explosion-impact-chemical-security-laws-162223516--politics.html

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#1

Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 9:14 AM

One of the questions that has occurred to me in regarding the use of Ammonia products and Fertilizers for terrorist projects, and also for production safety is why has somebody not looked for the addition of an inhibiting chemical that would not affect the qualities that make it a fertilizer, but would prevent it from being used for more sinister uses.

I am not enough of a chemist to provide an answer, but after a year on CR4 I am fully convinced that amongst the Gurus there is enough brilliance to solve this one easily, and then could hopefully have the powers that be legislate this to these faclitities.

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#2
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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 10:49 AM
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#3
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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 11:31 AM

This is a good idea. However, the article is specific to the trying to reduce the availability of IED materials in the Middle East, not to the general question of agriculture. While the iron sulfate addition may be beneficial to alkaline soils, what about other soils? (The standard answer in the US is "Consult your County Agent").

Iron sulfate + ammonium nitrate will not be marketable in some agricultural communities. Are there other additives possible?

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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 11:51 AM

I am not a farmer and I confess to not seeing a real cow until I was 10 years old, unless you count cow moose. However, if it works for alkaline soils, why would it not work in low pH soils. All it does is lower pH slightly and add iron that is good for most crops that do not prefer alkaline soils. Just don't use the enhanced ammonium nitrate fertilizers on soils to be used for alkaline loving plants. otherwise, I agree it is a great idea and can be implemented right away. However, the powers to be will talk and committee the project for the next decade or two. It would sure make it easier to trace sales of regular ammonia nitrate because it would be used under rare conditions.

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#5
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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 1:16 PM

It might make the low pH soils to acidic.

Seems like that wouldn't be a huge issue to over come though. In addition to mixing ammonium nitrate with iron sulfate, it seems like adding some carbonates (lime) for use in lower pH soils wouldn't be a big deal.

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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/10/2013 9:07 AM

So will regular ammonium-N lower pH. Low ph or acidic soils may be more of an issue in areas of high humidity or heavy rainfall because atmospheric pH could be low. Adding lime is likely needed in some areas and it will still be needed if the farmer uses the new Ammonium-N with FeSO4. Nothing really changes. If just adding a little iron sulfate at minimal cost improves the safety of the product, I say all production and imports of Ammonium nitrate should do the right thing and have the added iron sulfate. Anything to make it more difficult for the terrorist bent on killing people.

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#9
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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/10/2013 9:31 AM

Yes, application of AN fertilizer tends to lower soil pH.

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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 3:54 PM

Told you so,- I knew I would get some serious though and ideas on this - Thanks guys- I feel anything we can do to keep dangerous products out of badly motivated hands is progress- even if it is only one life saved it is a start- lets have more discussion

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Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

05/09/2013 3:56 PM

some nasty people have done this in the west also- can the two be separated?? and based on what I have heard the same idea might have worked at a production facility

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#10

Re: Quantitative Risk Analysis – How to Prevent Incidents like the Explosion in West, Texas

07/02/2013 10:36 AM

How do you anticipate human behavior in a quantitative manner?

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