Perspectives: Field Notes

A haphazard approach can hobble hazard reviews

Taking some simple steps can help you avoid common pitfalls in assessing changes

By Dirk Willard, contributing editor

The room grew tense as the reliability engineer complained that the condenser being discussed was slated to be replaced during the next turnaround. The simulator model, the basis of the whole project, didn’t include this change. What had been a plant hazard analysis (PHA) quickly degenerated into a process review.

This is an excellent example of what can go wrong during such evaluations. So, let’s look at what you can do to make your PHA or hazard and operability (HAZOP) study go smoothly.

First, carefully consider the basis for the process change — the reason for the review. What’s the purpose? What’re the options? Of course, the particular situation may limit the choices. Is there a way to avoid safety problems, simplify a process, or reduce hazards? For instance, Can you improve mixing in a reactor and make it smaller? Or Can you eliminate recirculation lines (reducing hazardous inventories)? Which option offers the lowest total cost? Is this the safest option? Consider summarizing the choices in a table. The design team should present these thoughts in a report with a buy-in from the project leader before scheduling a PHA or HAZOP.

With the solution in hand, next account for the plant’s preferences — e.g., for a particular type of flow meter or for RTDs instead of thermocouples. Don’t completely rely on company standards. After all, one unit at the site may prefer steam tracing while another may only accept electric tracing. If these choices pose new safety issues, they need to be considered before the safety review.

Another often missed hazard is scheduling. Can your process change be implemented all at once or will several plant outages be required? Can the plant operate safely with the interim changes? How will other changes in parallel projects affect yours?

Then, of course, there’s operator training — you’ll want to avoid gaps in training. You also should assess how a change will affect operator workload.

Now, you’re ready for the process and instrumentation drawings (P&IDs). First confirm the battery limits and make sure the P&ID you start with is the latest revision. Don’t crowd your P&IDs; leave plenty of room for notes and equipment. When more detail is needed, notes can refer to other documents. Make sure old bubbles are removed. Use color, if possible, to highlight the changes. Don’t be afraid to add a second or third sheet to your drawing set.

Finally, prepare your presentation. Utilize all team members effectively. Don’t assume everyone is familiar with your process or project. Here’s what each attendee will need: 1) P&IDs; 2) process flow diagrams; 3) a material balance; 4) mechanical information; 5) the alarm/trip schedule; 6) the process description; and 7) the purpose of the review and the process changes.

Have reference material on-hand for consideration by your team. For instance, provide a drawing of the entire facility with the area affected by the hazard review highlighted. If equipment will change, create a table comparing the old and the new items. Make available summaries of past PHAs and HAZOPs of the area and accidents with excerpts of concerns listed for discussion during the review if necessary. Time-line via tables the maintenance history of relevant equipment.

Now you’re ready to do your review — but guard against common mistakes.

Hazard reviews often focus too much on operations without considering maintenance. When a new threat appears on the horizon, operation engineers prefer to slap in another instrument rather than use the ones they have in a new way. This adds to the maintenance workload.

Another problem is what I call “the boogie man effect.” Hazard reviews tend to produce unrealistic solutions and imaginary fears. In one case, a caustic scrubber was proposed for a remote unloading facility. Maintaining the scrubber at the proper concentration proved difficult. It sat idle, unfilled, and became a haven for spiders.

Another pitfall is equipment pressure limits. Use the ASME-defined temperatures not the limits for alarms and trips. The code fixes maximum allowable working pressure (MAWP); trips prescribe maximum allowable operating pressure (MAOP). Trip settings change; avoid ones above 80% of relief settings because that’s the point when valves start to open.

Once the meeting gets started the facilitator needs to get everyone involved. One idea is to go around the table for the first hour asking for opinions from all. However, maintain discipline once the discussion is started. When a sidebar conversation goes too long, ask those involved to provide an opinion on the question at hand or for a contribution to the main discussion. Sometimes, sidebars produce enlightening ideas.

With a design approach that is methodical and with thoughtful planning in preparation for the PHA or HAZOP, this painful process can effectively serve its purpose.

More from this perspective...


Make Your Drawings Match Your Process

Outdated P&IDs can lead to tragedy


Make the Most of Contractors

Using hired help effectively starts by treating them as part of your team.


Make the Most of Electric Tracing

The technique offers benefits but demands attention to details


Make the most of newly hired, experienced engineers

Contributing Editor Dirk Willard reminds readers that an old dogs can learn new tricks and plants should keep this in mind when hiring new, yet experienced, engineers.


Making Your Process Operator-Proof

Senior Editor Dirk Willard discusses Shigeo Shingo's take on mistake-proofing, or Poke Yoke, if you speak Japanese. The practice suggests the following devices: eliminate — redesign, facilitate — guide, mitigate — lessen the damage caused by the error, or flag — identify the error.


Match the Flow Meter to the Service

Consider operating conditions not just specifications and price


Move Against Static Electricity

Discharges pose persistent perils at plants.


Operational Safety and Maintenance: Fear Ad Hoc Fixes

Interim solutions can lead to dire consequences.


Plant Safety: Leaks Don't Lie

Treat them as calls for action against the underlying problem.


Please Don’t Hire Me!

Some contracts simply aren’t worth winning.


Pressure tests can spur successful start-up

Push it: if it breaks it probably needed to be replaced, says Dirk Williard, in this month's Field Notes column. Doing so can help improve your processes.


Process modeling: Find the Right Balance

Eight simple rules can help ensure valid material balances.


Properly Estimate Engineering Hours

Don’t come up short on a project.


Properly Tackle Fluid Flow Problems

This requires far more than modeling software.


Protect Pumps and the Bottom Line

Setting an appropriate minimum flow avoids damage and excessive operating costs


Protect your electronics

Ignoring exposed electrical boxes can cost you a bundle, says Contributer Dirk Willard, in this month's Field Notes column.


Pumps: Check "Standard Conditions"

Otherwise you risk using the wrong value for density in calculations.


Reduce Your Energy Needs

Achieving savings may provide a powerful career boost.


Rely on an Ombudsman for a Smoother Project

Working with someone who speaks the operator’s language will avoid problems, according to Dirk Willard, in this month's Field Notes column.


Remember the old reliable orifice plate

The cost-effective dP flow meter is ideal for utility surveys, Senior Editor Dirk Willard says in this month's Chemical Processing Field Notes column.