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Forensic Engineering who specializes in Trusses/wood

Forensic Engineering who specializes in Trusses/wood

Forensic Engineering who specializes in Trusses/wood

(OP)
I have a few questions regarding how an engineer forensically exams trusses for heat damage. Are there any Forensic guys out there that specialize in trusses?

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

Wayne...I doubt there are any forensic guys who specialize in fire damaged trusses, but most of us in forensics have done a few of them.  Fortunately, they don't come around every day.

As noted in the other forum, here's what I would look for:

1.  Dimensional changes, mostly shrinkage due to drying
2.  Distress in fasteners and plates.  Have the plates pulled out?  Have the plates lost engagement?
3.  Amount of charring, depth of charring, and location of charring.
4.  Comparison of surrounding materials to get an idea of exposure temperature (did it melt certain plastics?  Did metals in the area expand or discolor?)
5.  Did excessive temperature cause sap bleed?  If so, how excessive?
6.  Is there any dead load deflection as a result of the elevated temperatures?
7.  Review fire department reports and records to discern time on site, involvement of the fire at first observation, approximate temperatures if measured, time it took to extinguish, whether water was continued on smoldering sections.
8.  Spalling of concrete materials near or adjacent to wood.
9.  Damage to metal straps/accessories for uplift.
10. Sample and observed cross sections of the wood under microscope to check for cellular structure affects.

I'm sure I've left off a few things, but these are things I've looked at in past evaluations of fire damage.  Most recent was in February of this year...testified in Tallahassee on structural damage.

RE: Forensic Engineering who specializes in Trusses/wood

I've used an incremental borer which is a 'hollow' drill type of tool to take a core sample for microscopic examination. I haven't used it for small trusses, but have used it for large timber trusses damaged from both fire and dry-rot. I know they are still available because I had to have the borer replaced about a year ago. It was purchased from an outfit in one of the southeastern states (My borer is at the office and I don't recall the name).

Heat causes changes to the wood itself.  Initially the lumber is dessicated and then the constituents, primarily lignins and hemicelluloses start to break down.  Initially non-flammable components are released and then the reaction becomes exothermic (it generates heat and the reaction progresses on its own). Do a web search of destructive distillation. The chemical progression is fairly well documented.

It is possible to for the extent of pyrolysis to be determined by chemical analysis and depending on how serious the case progresses, it is possible to use similar undisturbed samples and test them by using controlled 'baking'. This is getting into some 'heavy' and costly forensics. Once you have a copy of the report from the insurance company's engineer, you may have to go this route.

I don't know how the insurance company's engineer works and if there is any bias.  When I do a report for an insurance company, I clearly state to the owner that although the report is for the insurance company that it is unbiased and that the report would essentially be the same had I been hired by the owner. If there is a bias and the report is flawed or biased, then you may have recourse through the professional licensing board (or whatever). I also inform the owner that the report is for the insurance company and that release of it is at their option. I have only had consistent difficulty with one insurance company. I'm driven by technical aspects and not client driven.

I note that Ron is licensed in your area and does forensic work. If you search the site, you can look to his other responses and he appears to be pretty knowlegable and thorough; you might consider retaining his services.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
Thanks Guys. BOAF meeting let out early today and I enjoyed a good cigar near AIA Brewing Company downtown St. Augustine. Sure is beautiful here.  Had a nice Guiness and watched the tourist spend their money.   

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

Wayne,
Glad you're enjoying the weekend..Yep, St. Augustine's a nice place. From A1A Ale Works looking across the Bridge of Lions and the inlet at sundown....nice!

I'm sipping a Landshark and watching the Gators win!

Ron

RE: Forensic Engineering who specializes in Trusses/wood

Ron and dik - always amazed at your knowledge.

 

RE: Forensic Engineering who specializes in Trusses/wood

JAE... surprising how much you forget in 40 years... other than a short period, I've been active with it... helps prevent 'oldtimers' disease...

 

RE: Forensic Engineering who specializes in Trusses/wood

Thanks, JAE...but I could write a book about what I don't know.

RE: Forensic Engineering who specializes in Trusses/wood

My incremental borer is manufactured/supplied by "Forrestry Suppliers Inc, out of Jackson, Miss. and Model 63415.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

I have always been taught that if wood is exposed to temps great than 150F - then breakdown begins.  Not sure how long a duration is required but I would assume the outer fibers would start to breakdown fairly quickly - like in minutes....and the outer fibers carry the highest tension/cpmpression loads in a truss or beam.

RE: Forensic Engineering who specializes in Trusses/wood

Mike:

You are correct about the lower temperature.  The wood starts to dry out and the lignin and hemicellulose starts to break down. It's not until you get an additional couple of hundred degrees that the chemical reaction becomes exothermic and combustion proceeds.  Up to the point of combustion the various components break down further until the reaction is 'self-sustaining'.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

I agree with dik.. the lower temperatures will cause some drying, but the real breakdown occurs as much higher temperatures...after all, roof surfaces in Florida often hit 150 degrees, so the wood sheathing and structure get some long exposure to elevated temperatures.

RE: Forensic Engineering who specializes in Trusses/wood

Alligator pattern is another sure fire (nice pun) way to spot structural damage in the wood.

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
I was travelling and missed all the posts.  A wealth of information. I'll look for the alligator patterns.  I would imagine that 900 degrees for over 45 minutes is hot enough and long enough... And, I agree... Ron and Dik are a wealth of information. Thanks for the additional info Mike and FSS. On the road again this week.   

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

Even at lower temperatures the wood starts to breakdown. Carbon dioxide as well as water vapour is released.  In addition, depending on the species, Acetic acid (C2(H20)2, with a boiling point of approx 120C and Formic acid (CH2)2) with a boiling point of approx 100C are released. (note the low boiling point and the combination of carbon and water molecules). In addition, some of the natural extractives, lignum materials and oils are evaporated from some species. This has the effect of reducing strength, impact and decay resistance.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

That should be lignins... sorry... I have a couple of samples of lignum vitae, was thinking about extractives and the wrong word emerged...

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
Here's hoping that the Forensic Engineer hired by the insurance company knows even a fraction of what you guys do.  Last I heard, the group specialized in sinkholes, so lets see what happens.  I'm printing out all of your comments and trying to learn more.  But, I'm also trying to work at the same time, so this has been a lot. The more expert opinions I have to review, the better I feel that I have a good perspective.  I know I have the damage, they just don't want to acknowledge it.   

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

I didn't know the chemical formulae off the top, but have a technical appendix inclusion that describes what happens with pyrolysis... just added it to show that the compounds are a mix of oxygen, hydrogen and carbon... and that the BP is quite low.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

Wayne,
Sounds like they've engaged one of a couple of testing labs in your area that have primary experience in evaluating soil conditions in Polk, Hardee and surrounding counties.  That's fine, as long as the person involved is capable of evaluating structural materials.  One of those firms in that area has some reasonably good people and can do this type of evaluation.  The other significant one does not.  I hope you got the good one!

I'm waiting to see their report.  Should be interesting.

Ron

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
Ron, I'm anxious to see the report myself.  I'm in DC. Went to visit Mt. Vernon today. Talk about code compliance issues. It's incredible here.  Weather is cool and the restaurants are diverse. Only problem - can't park the Escalade anywhere. Apparently, DC is into smaller vehicles. Parking the car is $38 a night.  I asked if I could let a homeless person sleep in it for the week I'm here. Apparently, that's against the rules.  On the other post, I have someone questioning the code issue... I'm about the reply to him.  I'd appreciate your and Dik's opinion on it.

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

It would be great to see it. I'm curious about the duration of fire and the temperatures.  I hope these are correct and can be substantiated...

Do you have photographs of the damage? and have you taken any core samples or coupons? Things change with time. A significant part of the 'musty' burn smell is caused by a fungus that 'lives' in/on charred/burned material.

You might have a commercial truss engineer (possibly the people that supplied the truss) take a look, too and offer an opinion. He can direct you to the best place to take a sample without compromising the truss and you can likely get a 'plug' cutter drill from a local hardware store.

Your engineer might be into this and as a 'heads up'. I don't know about Ron's approach, but when I take samples, the first sample is one of the container/bag that I'm collecting stuff in... just to provide a 'background' if the issue of 'contaminating' samples comes up.

Dik

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
Dik, are you saying I should have taken a sample earlier? Is it too late?  I can have someone go out this week. Yes, we have pictures.  The proof of the temp and duration is in the fire report and my wife was shopping at the time and I have had her save the receipts.  I'm not sure what other proof there could be.  

You are like the CSI of wood...  

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

RE: Forensic Engineering who specializes in Trusses/wood

dik...I agree with the sampling protocol...we do that as well.  It gives us the ability to discreetly smirk when opposing counsel brings up the issue of sample contamination.

Wayne, one other significant point you have to consider is that of real estate disclosure.  If you ever decide to sell your house, you will have to disclose the damage if it is unrepaired.  It will get flagged and highlighted in a "home inspection" report obtained by the buyer.  Fire damage is sometimes a deal killer, even after cleanup.  Unrepaired fire damage is a clear deal killer, so the insurance company is compromising your ability to receive fair market value for your house or to possibly even sell your house.  Tell them to pay for the repairs or buy your house since you can't sell it!!

RE: Forensic Engineering who specializes in Trusses/wood

Wayne... I like to take samples and like to take them ASAP... best to check with your engineer or your forensic dude for sampling. Depending on the condition or tech response from the insurance company, you may not need them.

Photographs of the worst? truss damage and a macro of one of the most discoloured/damaged truss plates would be interesting.

NFPA also has a protocol for fire investigations... if your engineer isn't using it, he may take a gander.

Next to 'Reality Programs', CSI programs p*ss me off, big time, and I don't normally get riled. Worse than Rap music(?). I do, however, like the fraggles...

Dik

RE: Forensic Engineering who specializes in Trusses/wood

(OP)
fraggles?  Dik... I'll have to send you a box set of the fraggles... unless, of course, you already have it.  You're too funny.

Wayne D. Smith, Jr., CBO, MCP, CEAP, LEED AP

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