Plant Layout : Risk Based Layout or Not??

[roshan]

Dear friends,

We are in the initial stages of the FEED for a sour gas facility (3.5 % H2S, 1100 psia). Our company has a recommended practice for equipment spacing. It says that the safety distances provided are the optimum. But, our consultant is recommending a risk based approach to define the plant layout. They have done some initial toxic release studies, and based on that they recommend that we expand the current layout to a bigger footprint, to ensure that the toxic risk levels are ALARP.

Could you please tell me how the other operating companies are addressing this issue of defining a plant layout, at the first pass? Specifically, I want to know - if its a sour gas facility, is essential to adhere to a risk based layout from the first pass itself? are there any standards available setting up the requirements for this risk based layout method?? Any help would be much appreciated.
thanks, Roshan

[safetyuser]

Dear friends,

We are in the initial stages of the FEED for a sour gas facility (3.5 % H2S, 1100 psia). Our company has a recommended practice for equipment spacing. It says that the safety distances provided are the optimum. But, our consultant is recommending a risk based approach to define the plant layout. They have done some initial toxic release studies, and based on that they recommend that we expand the current layout to a bigger footprint, to ensure that the toxic risk levels are ALARP.

Could you please tell me how the other operating companies are addressing this issue of defining a plant layout, at the first pass? Specifically, I want to know - if its a sour gas facility, is essential to adhere to a risk based layout from the first pass itself? are there any standards available setting up the requirements for this risk based layout method?? Any help would be much appreciated.
thanks, Roshan

dear roshan

with 3.5 % H2S at 1100 psia I would be very very happy to have such a consultant like yours who press for risk-based approach to layout since the early stage of design ...

Moreover, it seems to me by your question that your Company did not set an Hazard Management Process: if they would have, they would state clearly what are the steps to demonstrate the risk is ALARP level and I hardly figure how alarp would be reached if no risk-based considerations have been carried out when taking care of inherent safety principles

[roshan]

Dear safetyuser,

Thanks very much for your input..yes, we indeed have all the standards for hazards and risks management. But, afaik, they nowhere specify that your plant layout has to be driven by a risk analyis (based on toxic gas dispersion studies). the typical approach would be to generate the first pass plant layout based on the recommended spacing charts, and then subject this to a QRA at the end of the basic engg. phase.

Some operators opine that the reduction in risk levels within the plant are more effectively achieved by measures like inspection, maintenance and protective systems, rather than spreading the layout extensively. They feel that there is unlikely to be any significant reduction in the knock on potential by variations within the practicable separation distances. Also very small release scenarios like small flange leaks or small pump seal failures could potentially lead to the requirement of very large plot areas.

Guys, please chip in with your thoughts, as well..all inputs will be much appreciated!!

[safetyuser]

roshan, let me disagree with "some operators" opinion

you are involved in a FEED design, not in a Operational phase and I believe your Safety input to the Project should be to drive risks alarp since the very early stage of the design

Anyway, you can find a lot of very very very very interesting books and reference within this forum about inherent safe principles to be applied during the design: it is the first time I hear about disregarding these fundamentals for the benefit of inspection, maintenance and protective systems (which are themselves part of a risk-based approach to safety)

Anyway I don't want annoy you with these issues, simply to warn that if "very small release scenarios like small flange leaks or small pump seal failures could potentially lead to the requirement of very large plot areas" means that serious safety and health issues do exist in your design and somebody should take seriously action NOW, to be confident that the designer will deliver a safe and operable plant to the final user. Obviously, risk-based approach means also a balance between costs and benefits for each option to be proposed, but this shall a be a clear and transparent process to be demonstrated by means of documented assessment. They only "feel" there is unlikely benefit but maybe they cannot support with evidence.

[safetyuser]

I' m pleased to share with you the ERCB H2S model and user book at this following link:

[link Point to another website Only the registered members can access]


ERCB H2S Model


The Canadian Energy Resources Conservation Board (ERCB) has a stringent regulatory framework that is governed by principles aimed at protecting the public and environment from harm through responsible petroleum operations. These principles are embodied in the many ERCB directives that together form the components of the Emergency Management System—

prevention, mitigation, surveillance and enforcement, and investigation

The November 2008 edition of

Directive 071 updates and replaces the July 2008 edition. It includes updates and clarifications, including those resulting from stakeholder feedback

[link Point to another website Only the registered members can access]

[link Point to another website Only the registered members can access]

[CLPC]

Roshan
in relation with consequence modeling and IRPA Qalculation, it seams that the need to extend the space between your equipments is to increase the air movement rate in your plant. it may reduce the toxic concentration in the air and reduce the radius of fatality distance. If this is the case none of inspection and maintenance can do this. Inspection of your pressurized equipment may reduce the leak frequency of your process equipment. but you have to demonstrate it with the Quantitative Risk Based Inspection. maintenance of your shutdown system (Functional Testing) may reduce the PFD of your shutdown system but you have demonstrate it with SIL verification study.

[CLPC]

Roshan
in relation with consequence modeling and IRPA Qalculation, it seams that the need to extend the space between your equipments is to increase the air movement rate in your plant. it may reduce the toxic concentration in the air and reduce the radius of fatality distance. If this is the case none of inspection and maintenance can do this. Inspection of your pressurized equipment may reduce the leak frequency of your process equipment. but you have to demonstrate it with the Quantitative Risk Based Inspection. maintenance of your shutdown system (Functional Testing) may reduce the PFD of your shutdown system but you have demonstrate it with SIL verification study.

[roshan]

Safetyuser,

Thanks very much for your kind efforts. The documents that you have provided are quite useful in this regard. Very much appreciated.

Roshan