Defining Risk In Process Safety Management

Process safety is intended to prevent unwanted conditions or releases of hazardous chemicals, especially into locations that could expose employees and communities to serious health hazards.

By: Sandy Smith

An effective process safety management program requires a systematic approach to evaluating the whole process, including the process design, technology, operational and maintenance activities and procedures, emergency preparedness plans and procedures, training programs and other elements that impact the process, said Julien Chouinard during his ASC 2013 session, “Process Safety: What EHS Managers Should Know About Standards, Technology and Best Practices.

Chouinard, who’s the business director for critical control at Rockwell Automation, opened his session with some grim reminders of process safety failures. These incidents, he added, served as wake up calls for the UK, Europe, Asia and the United States:

1974: Flixborough (UK) – 28 deaths, > 100 injuries
1976: Seveso (Italy) – Major dioxin release
1984: Bhopal (India) – > 3,000 deaths, 200,000 injuries
1988: Piper Alpha (UK) – 167 deaths, destruction of platform
1989: Pasadena (Texas) – 23 deaths, > 130 injuries
2005: Texas City (Texas) – 15 deaths, 180 injuries
2010: Deepwater Horizon platform (Gulf of Mexico) – 11 deaths, 210 million-gallon oil spill

Sharing information from the UK Health and Safety Executive, he said control system incidents occur for several reasons:

44 percent incorrect and incomplete specification
20 percent changes after commissioning
15 percent operations and maintenance
15 percent design and implementation
6 percent installation and commissioning

“Functional safety standards address all of these issues,” he added.

How Process Safety Works

What is process safety? Essentially, when you are doing process control, said Chouinard, you ideally have everything under control. You have a piece of equipment that you are trying to maintain within operational ranges. For example, if you have pressure in a system, you want to maintain that pressure within a given range.

There is a basic process control system (BPCS) that essentially looks at the parameters and controls the pressure within the expected range. This system is a series of interventions that the process goes through should things get out of the expected range.

The first step is operator intervention. Alarms will ring and the operator will look at the actual process and try to act – based on the training he or she has received – to reduce the conditions or keep the conditions within control.

If the operator cannot do this, then the emergency shutdown system should kick in. It will trip and try to shut down the process or even the entire plant. Chances are, this will work.

If this doesn’t work, said Chouinard, then the relief valve will start releasing the pressure in the system. “At this point, we’re not protecting or preventing the events from occurring, we’re trying to contain the problem … [and] help prevent a catastrophe from happening,” he pointed out.

“When we talk about process safety, we talk about trying to keep the system in the prevention zone and never have to go to the mitigation zone. However, we have to plan for all possibilities,” said Chouinard.

He said the other type of system, other than the BPCS, is the safety instrumented system (SIS), which is “composed of sensors, logic solvers and final control elements for the purpose of taking the process to a safe state when pre-determined conditions are violated.”

So, he said, facilities have a basic process control system and a second system that will monitor the same pressure levels at the BPCS but at some given point, the SIS will decide to use the shut down valve to make sure the pressure doesn’t reach a level where that vessel can explode.

“SIS is passive. It doesn’t do anything,” said Chouinard. “It might sit there for six years without doing anything. But at some point, the pressure might go up and it will have to kick in.”

See the rest of this story here: http://ehstoday.com/safety/asc-2013-defining-risk-process-safety?page=3

Source: EHS Today®