I recently participated in a PHA for a large flammable liquids process and during the “facility siting” portion of the PHA we took a detailed tour of the process. During which, several significant “impact” hazards were identified. Of course, the long-time engineering manager (40 plus years of fine service at the facility) quickly went to the “it has been that way for 50+ years and no one has hit the pipe/pipe support or dropped a load on the pipe/pipe support“. So the question is… How much “safety credit” should we give based on a 50 year run of no damage/incidents when we can plainly see that the scenario has a high potential?
It must be said before we go any further that a pipe support that has black marks on it or leaning from obvious impacts MUST come into play in the assessment. Merely not ripping down a pipe bridge over 50 years, but there are all kinds of indicators the bridge has been impacted over the years is NOT process safety. In this case, the facilitator rightfully challenged the engineering manager and asked him to show the team that the pipe bridge was built to withstand a horizontal force equal to that of a raised forklift mast. Do you hear the crickets chirping!!!!
So for the sake of discussion, let’s say there is NO evidence the pipe bridge, piping, piping supports, etc. have been impacted. Everything is in fine working order. But the PHA team recognizes that the main pipe bridge from the tank farm to the process goes over top the main roadway. This means all kinds of vehicles travel under the pipe bridge and by the pipe bridge columns on a daily basis. The engineering department can not provide any evidence that the height of vehicle(s) permitted to travel under the bridge was considered when it was built. No one knows why it is the height it is and why it was put where it was. So do we feel comfortable that nothing has happened in the past 50 years; so comfortable that we leave things be and move on in our assessment? I would say hell no!
As a facilitator, we need to look beyond the experiences with this single pipe bridge. Have we ever seen a bridge, overhead pipe, etc. struck by a vehicle traveling under it? Yes, you would be hard pressed to find an adult who has not seen or heard of such incident occurring. So the challenge comes down to this “what can the facility provide that can demonstrate they have controls in place that has prevented this pipe bridge and/or its support columns from being struck”? Keeping in mind this same logic should be applied to all equipment handling HHC/EHS that have the potential for impact by vehicles/powered equipment, etc.
At what level would we feel comfortable saying they are “managing this risk appropriately”? That all depends on the HHC/EHS and the size and number of pipes in the pipe bridge, but for starters I look for the following:
- Guarding (Engineering Control) is fundamental. If vehicles are permitted to pass by/under this structure and this structure is deemed “safety critical” then it is ALWAYS WISE to provide a substantial vehicle barrier between the structure impact zones and the path(s) of the vehicles. These barriers need to be significant so as to be effective for the size of vehicles it is exposed to. Bollards are a common tool used at ground level where the potential for impact is much higher. Guarding the horizontal run of pipe over the roadway is a bit trickier, but should ALWAYS be considered even when only one pipe contains the HHC/EHS. Multiple pipes carrying HHC/EHS can raise the severity of the incident exponentially and thus require more consideration. Anyone who has driven through a fast food drive-by window has seen these types of guards. I always like to say that if McDonald’s and Wendy’s determined the need to protect their awning, how do we justify not protecting our HHC/EHS piping? The best option is to weld a substantial beam out about 3-4′ from the pipe bridge at a height that any vehicle that could impact the pipes or the overhead bridge structure would hit it first. We are not trying to stop the vehicle in its tracks, but we want the driver to know he/she has hit something so they will stop.
- Administrative controls can add layers of protection ON TOP of the engineering controls.
- Signage stating the height of the pipe bridge is the most basic need for any overhead obstructions crossing a roadway. But often times there is no sign and maybe one or two people on the site even know the actual height! We have even found signs with INCORRECT data placed on the incorrect pipe bridge (contractor was either told wrong or got the signs mixed up!). So signs are needed but are NOT the sole solution for our HHC/EHS pipe bridges!
- Have an “oversized load” procedure for the facility. Some larger chemical facilities will have a policy and procedure for how trucks carrying loads at a certain height and width will move within the facility. A recent startup I was involved with, the plant engineer built all the pipe bridges at the same heights as interstate overpasses are now built to. This was documented in his design drawings as a “note”. Knowing the plants future expansion plans, he also designated a special route for the new equipment so that it would avoid as many overhead pipe bridges and culverts, etc. They also had a procedure for how an “oversized load” would be dealt with by security, engineering department, operations, and safety. He took the same “escort” procedures and modified them for the in-plant movement of these trucks. It was an impressive display, one that few will forget after witnessing. Of course, this engineer had lived through a pipe bridge incident earlier in his career so he was motivated!
- Include in your contractor safety orientation section about vehicle safety the requirements to bring on site trucks with dump beds that raise or oversized equipment not permitted on state roadways.
Bottom line is that if there are no engineering or administrative controls in place to PREVENT these structures from being impacted by vehicles than ZERO (0) credit should be given in the PHA. This should then force us to recommend that some type of appropriate vehicle barrier be installed or a means to prevent future traffic in the area. Yes, sometimes it is cheaper and easier to place a barrier to prevent vehicles from even getting near the safety critical structure (i.e. shutting down the pathway).
I will leave you with this challenge… ask your engineering group what the flow of the HHC/EHS is in those overhead pipe racks and add up the gallons/per minute and see how much HHC/EHS can be on the ground in one minute if the entire rack is to be compromised (has happened many times before and it will happen again – I can promise that!). Feel free to consider your safety systems in place for this scenario as long as they are DOCUMENTED safety systems in your PSI and MI programs! Now ask yourself….
- What if this material is a flammable liquid/gas and the truck that causes the incident is jammed under the bridge with this flammable product forming a vapor cloud what do we believe can happen next? Is the area under your pipe bridges included in your Electrical Classification documentation – it should be considered, especially if it is flanged pipe! What safety systems are in place to address this release at these locations? Do I have adequate fire fighting capabilities to handle this incident? Can I shutdown flows remotely? etc.
- What if the HHC/EHS is toxic with a high vapor pressure? I have done several RMP “worst-case release scenarios” where a large diameter pipe under high pressure was, in fact, the WCS due to its location at the facility and proximity to the property line. This would add a significant consideration to how we protect this pipe bridge! But even 12″ duct work going to a scrubber that is NOT made of steel and is on the outside of the pipe bridge has to be considered as “risky”. Often times we see something within the vehicle that is simply placed in a vertical position rather than laying down (i.e. ladder) that will strike the pipe/duct work. Fiber re-enforced piping just can not withstand the impact of a ladder rail traveling at 10-15 mph.
- Are there any “incompatibles” traveling together via the pipe rack that in such an incident would find their way to react?
Remember the “flower truck” incident at the ammonia terminal? It can happen to anyone who does not have the proper controls in place to PREVENT, PROTECT, and MITIGATE the incident.