Forensic Engineers and Consultants

Tag Archive: injury investigation

  1. P&ID’s, If You Please – Piping and Instrumentation Diagrams Explained

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    When investigating an industrial incident, one piece of information I always ask for is the relevant P&ID’s for the process.  P&ID stands for Piping and Instrumentation Diagram and is defined as “A schematic diagram of the relationship between instruments, controllers, piping, and system equipment.” A set of P&ID’s for an entire facility allows you to trace the entire manufacturing process from raw material unloading to finished product loadout, including utilities like steam, water, fuel, and air. That’s great information to have, but isn’t especially useful in an incident investigation. However, the information from the P&ID’s covering the vessel or vessels involved in an incident can be very useful.

    In a previous blog, I wrote about the distributed control systems (DCS) that manufacturers use to monitor and store process data such as temperatures, pressures and flow rates, etc.  The P&ID for those processes will show where these measurements are taken. Not physically, as in, “the flow meter is located on the northwest corner of the third floor”, but relative to the rest of the process, “the flowmeter is located downstream of the discharge pump and upstream of the split between Vessel A and Vessel B.”

    The symbology and abbreviations used on P&ID’s typically come from one of two standards: “ANSI/ISA-5.1 Instrumentation Symbols and Identification” or “PIP PIC001 Piping and Instrumentation Diagram Documentation Criteria.” These are both real page-turners!  Actually, they are jam-packed with useful information that is, by definition, pretty dry.  They lay the groundwork for how to read the instrument identifications (tag numbers) on the drawings.  Part of the symbology shows whether a measurement point is being tracked by the DCS, and therefore, useful in investigations.

    P&ID with marked tag numbers

    P&ID’s also let you see the control loops in a process.  A control loop is a collection of equipment that will control a part of a process.  Let’s say you have six identical reactors, then TIC-100 could be a temperature indicating controller on Reactor 1, TIC-200 on Reactor 2.  The P&ID will show that the temperature controller for each reactor works by opening or closing the valve in the steam supply to the reactor’s heater.  The math behind how the controllers determine when and how much to move the valve opening is emotionally scarring, by the way.

    In another example, let’s look at a tank that has a level controller. It controlled the tank level by sending a signal to a flow controller in the discharge line.  This signal adjusted the setpoint of the flow controller. To keep the level at 50% required an outflow of 100 lb/min of material which normally required the flow control valve to be 35% open.  Over time, the flow stayed the same to control the level, but the valve opening went from 35% up to 100%, indicating something was impeding flow from the tank.  Subsequently, the valve in the discharge line stayed at 100% but the flow started dropping off from the 100 lb/min needed to keep the level at 50%, so the level started to rise.  If this was a tank overflow incident I was investigating, then the P&ID’s would show me the tags for which I would request process data from the DCS.  That data would tell the story written above.

    An example of a control loop and tag numbers

    In addition to providing information about control loops, P&IDs are incredibly useful when authoring a Lockout/Tagout or Confined Space Entry procedures.  When I was in manufacturing, we had reactors that were twelve feet in diameter and over one hundred feet tall.  To physically survey something that big to try to find all the isolation points would be, as my husband would say, a “low percentage move.”  Instead, pull out a P&ID and every pipe leading to and from a vessel is right in front of you.  Feed lines and product outflow are no brainers, but would you have missed the nitrogen blanket feed line at the top of the vessel in the field?  Maybe.

    P&ID’s are identified in the OSHA PSM standard (29CFR 1910.119) as part of the process safety information that must be compiled before any hazard analysis is performed (reviews included). Manufacturing processes covered under the PSM standard, must make sure their P&ID’s are accurate and up to date as part of the ‘Management of Change’ requirement of PSM.

    So if you ever find yourself needing to investigate an incident at a manufacturing facility make sure to ask for the P&ID’s, or your expert surely will.

    As President of The Warren Group, Jennifer Morningstar, B.S.Ch.E, P.E., CFEI, has over 20 years of engineering experience. Her areas of emphasis include chemical release & exposure, OSHA compliance, boiler systems, industrial accident investigation, fires & explosions, product liability and scope of damage/cost to repair analyses. She spent 16 years working at a polyethylene terephthalate (PET) manufacturer.  She is an OSHA-trained Process Hazard Analysis study leader and completed Root Cause Failure Analysis training to become an Incident Investigator. Jennifer authored procedures for lockout/tagout and confined space entry. She has experience as an energy management consultant in a variety of industries including mineral extraction, pulp & paper, animal harvesting & packaging (including rendering) and grain milling.  Jennifer holds a Bachelor of Science Degree in Chemical Engineering from Virginia Polytechnic Institute and State University as well as a Master of Business Administration from the University of South Carolina.

     

  2. The Role of Interlocking Guards in Injury Prevention

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    In the three-part series on the CE mark, we scratched the surface of some of the requirements an equipment manufacturer must meet in order to earn this designation. Part three of the series dealt with some of the requirements for the design of a guard.  One of the items for consideration with the design of a guard is the frequency that someone will need to access the area protected by the guard.  If access is needed on a routine basis, often defined as more than once per shift, the guard needs to be designed to be movable instead of fixed.  Movable is defined as able to be opened without the use of tools.  Otherwise the frustration and time requirements of obtaining tools and removing a fixed guard will often lead to the guard being discarded. (more…)

  3. The Paths of Chemical Exposure

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    The Safety Hierarchy states that hazards should be mitigated first by engineering controls, secondly by guarding, and lastly by warning/training.  When the first two, engineering controls and guards, fail in a manufacturing setting, a chemical release could occur. A forensic chemical engineer can help determine the root cause of that failure. (more…)

  4. Don’t Get Burned With Your Gas Grill!

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    If there is one thing Americans can agree upon, it is the enjoyment that comes from an outdoor barbeque.  Whether a summertime cookout or a fall BBQ to watch a football game, we all love the fun and fellowship that comes from sharing a meal that was prepared outdoors on a grill or smoker.  In fact, 64% of Americans own a grill or smoker.  The great majority of these are LP fueled gas grills with comparatively few natural gas fired grills.  These products can be enjoyed safely when designed, installed, and used in a proper manner.  However, given the grill’s use of flammable fuel gas and high temperatures, the potential exists for things to go wrong and result in burn injuries or uncontained fires that spread to the surroundings. (more…)

  5. What’s Behind That CE Mark Part Three, Machine Guard Requirements

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    In the first blog in this series, we discussed the story behind the CE mark, the Machinery Directive, and the associated requirements regarding the design, production, and sale of machinery bearing the mark. The second blog discussed a cornerstone of safer machine design, the risk assessment. This installment will discuss another crucial piece of the safety puzzle, machine guard design. (more…)

  6. The CE Mark and What Should It Mean to You? Part Two

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    In the previous blog (Part One) we discussed the backstory behind the two stylized letters CE and what it means to the design of machinery bearing the mark.   We outlined some of the requirements of the “Machinery Directive” (MD) which include what are known as “Essential Health and Safety Requirements.” The Essential Health and Safety Requirements incorporate an iterative risk reduction process during design that takes into account (more…)

  7. Collision Reconstruction – Time Distance

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    A common car crash is when one vehicle makes a turn or pulls out in front of another vehicle. Normally, without the accident, the vehicles only cross paths for milliseconds. When the collision occurs it’s no doubt because both vehicles try to occupy the same space at the same moment. The question is often “who is at fault?”. (more…)

  8. Water in the Light Fixtures??? How HVAC Defects Appear in Strange Places

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    One of my more interesting calls and subsequent forensic investigations was regarding water accumulating inside of 2X4 fluorescent light fixtures in a suspended ceiling of a secondary school in South Carolina.

    The client called and indicated that the metal chassis of the lights were sweating and generating enough water to accumulate on the diffuser lens of the lights.  Obviously, an on-site investigation was in order! (more…)

  9. Product Design is Critical to Consumer Safety

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    As the holiday season nears, thoughts turn to wonderful home-cooked meals with family.  Few things in life are more pleasurable than a traditional holiday turkey feast. Yet for an unfortunate few, holiday meal time can turn tragic if a turkey frying accident occurs.   While fried turkeys may be tasty, many fire safety experts feel that the reward is not worth the risk.  (more…)

  10. Over the Hill

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    When traveling down the roadway, a lot of things must be considered. While things that can be seen are obvious concerns, things that cannot be seen pose a threat too. Blind hillcrests leave drivers guessing “what’s on the other side”. Regardless of their intentions, before drivers make a maneuver, they should pay extra attention to blind hill crests. In a collision that occurs just over a hillcrest, where one driver is attempting to continue straight as the other is attempting to make a left-hand turn, many times the investigating officer arrives at a common conclusion. Failure to yield right of way charges are often applied to the driver making the turn; however, are these charges applicable? (more…)

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