Forensic Engineers and Consultants


Hail Isn’t Cool

Hail property damage is frequently reported after an HVAC service call.  Building owners are often unaware there is damage until the power bill starts trending higher and the HVAC system is simply not cooling effectively. Take look at the fins! The National Weather Service reported over $722 million in property damage from hail in 2018.  Based on NWS data, hail caused more property damage than tornadoes or thunderstorms.  Only Tropical Storms/Hurricanes at $12 billion, coastal storms at $1 billion and flooding at $1 billion were more costly than hail to property.

One of the items very susceptible to damage is the HVAC system.  The heat that is removed from the interior of a building must be rejected to the environment.   As such the HVAC system is placed where it can have unhindered access to outdoor air in order to function properly.  This often results in the unit being placed in a large open space such as a rooftop, making it susceptible to damage such as hail.

An air conditioning or HVAC system must reject the heat it removes from a building to the environment.  This rejection of heat to the environment is often accomplished by an air-cooled condensing unit which contains copper or aluminum tubes (coils) bonded to aluminum fins.  The coils and especially the fins are very thin to promote heat transfer between the refrigerant inside the coils and the air outside the coils rushing through the fins.  These fins measure around 0.006 of an inch in thickness, with a sheet of standard printer paper measuring 0.0035 of an inch.  So, the fins are roughly the thickness of two sheets of paper!

BEFORE COMBING                    |         AFTER COMBINGHVAC hail damage coils fins                                         

HVAC Condensing Unit Coil and Fins, both before and after combing. Fins are typically made of thin aluminum roughly the size of two sheets of paper.

Consequently, fins can be easily damaged by impact forces such as those generated in a hailstorm.  The image below shows damage to a condensing unit caused by hail.

hail-damage-central-air AE Mechanical Services, Inc.-Recovered englarged

Condensing Unit with Hail Damage

In this case the damage was minor, and the actual performance of the condensing unit was likely not diminished.  This damage can be repaired by “combing” the fins.   The tool, available commercially from many sources, is just as the name implies; a comb to straighten bent fins.  The tool must match the fins per inch for the respective coil and the technician must use care in the process, but the fins can be returned to a near factory state.Fin comb in use - Source EbayFin Comb in use

Fin Straightening Comb for multiple coils

Fin Straightening Comb for multiple coils

Often combing the fins will result in a return to full factory performance without requiring the replacement of the condenser coil.  Even examples where the fins have been almost completely blinded due to vandalism have responded well to repair by this combing method.  While the task of combing the fins may result in 1 – 2 hours of a technician’s time depending on unit size and the extent of the damage, the labor and parts savings over coil replacement can justify this expense.  If the actual coils themselves have sustained impact damage and not just the fins, this might not be the repair for you.  In the case of damage to the coil, replacement may be the best option to return the unit to factory performance. Property damage claims may or may not be inflated due to a quick decision to replace the coil or the entire unit rather than the tedious process of combing the coil fins, driving up the cost.

With condensing unit coils known to be susceptible to damage and hail being a very real threat, what options are out there to protect an HVAC investment?  One simple, but often missed item is to specify coil guards, often called “hail guards” on all condensing units.  Higher end residential condensing units often have them installed to protect the coil not as much from hail but routine household threats such as string trimmers, debris thrown by lawnmowers, and vandalism.

Rooftop HVAC units, however, aren’t likely to be damaged by routine activities such as mowing the lawn.   Access to the building roof area is often limited to maintenance personnel so vandalism is often reduced compared to a ground mounted unit.   Coil guards are not factory installed on many commercial units but are optional.  They should be specified in the bid package if the job is being competitively bid or they will likely not be included in the job.   See the figure below for factory installed hail guards.

hail-guard 2

Rooftop HVAC unit with suggested “hail guards”

With hail a heavy hitter for property damage, a little prevention in the form of hail guards for a building’s HVAC units will go a long way and provide some protection from vandalism.  If hail damage or even vandalism does occur but only impacts the fins and not the coil; combing the fins can be a cost effective and satisfactory repair to get the HVAC system running efficiently again.

Chad Jones, PE has a Bachelor of Science in Mechanical Engineering from Clemson University. Chad has over 23 years of engineering experience including mechanical, process, and manufacturing engineering. He participated in and led industrial incident investigations and participated in in-depth process safety audits. This work has included equipment design, machine safeguarding, cost estimating and safety compliance.  Chad also has over 10 years of commercial, industrial, and residential HVAC and plumbing design experience.


worn safetybelt

Belted or Unbelted? That is the Question!


Did the driver or passenger do what they could do to protect themselves by wearing their seatbelt? There are ways to determine if the safety-belt was being used. Most modern vehicles have a computer-controlled safety system that makes decisions based on an algorithm. That algorithm uses information such as change in speed and the direction of force to determine what to do.  That data not only tells how fast the vehicle was traveling and if the brakes were applied, but also records the driver’s or passenger’s safety-belt status. This is a great way to start an investigation but should not be solely considered as the fact that the belt was used; other evidence needs to be gathered to support the data.

worn safetybelt

cut webbing





The belt on the left is frazzled and worn; the belt on the right has been cut by the First Responders to remove the occupant.

When EMS arrives on the collision scene and finds an injured occupant belted in the vehicle, they typically don’t unlatch the belt to remove them from the seat; they cut the webbing. If this happens, the webbing has a smooth edge and the latch-plate is in the latch. Do not confuse torn or worn webbing with cut webbing. The cut webbing will have a smooth edge whereas broken or worn webbing will be ragged edged.  It should also be noted that, depending on the damage to the B-pillar (the second post from the front that supports the vehicle’s roof) or even if the first responder uses mechanical means to cut the vehicle open to gain access to the occupant(s), the webbing can be cut smooth. Therefore, look for the latch-plate still in the latch.

latchplate in buckle

The latch-plate is still in the latch and the webbing is unthreaded:  EMS cut the webbing to remove this occupant.

If the belt was latched the webbing may not retract back after the crash.  In these situations, the belt will have slack enough to fit around the occupant; if they had it buckled behind them, the belt, when latched, will not leave enough room for a person to fit. In a similar fashion, if the belt was not being used and the pretensioners fired locking the belt retractor the belt will be extremely tight up against the B-pillar.

pretentioners lockedThe seatbelt retractor locked leaving slack where the webbing was across the driver.

Other things to search for are stretches, curling, or transfer to the webbing.  As the webbing pulls through the loop of the latch plate and/or the loop ring on the B-pillar, it is possible for the webbing  to stretch, the heat of the frictional contact with the loop to cause curling, and/or the plastic cover to the loop to leave a transfer on the belt.   When these things happen, there is typically a noticeable change in the texture of the webbing that can be seen and felt.

webbing burnPlastic transfer from the loop on the B-post burned onto the webbing.

There are more things that can be looked at in addition to the recorded data and the damage to the seatbelt, such as occupant injury, airbag status and collision damage to the vehicle.  The seatbelt aspect of a collision reconstruction may be used to determine whether the seatbelt’s physical evidence does or does not line up with the rest of the story; such as if an unbelted person contributed to their own injury by not buckling up or if someone is claiming to be in the vehicle but the physical evidence and data shows the passenger’s seat was unoccupied.

Aaron (Al) Duncan II, ACTAR, is a vehicle collision reconstructionist with Warren and President of SCARS. Prior to joining Warren, he worked for 23 years as a South Carolina Highway Patrol Trooper to include 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) member. Al is accredited as a Traffic Accident Reconstructionist by The Accreditation Commission for Traffic Accident Reconstruction. He investigated in excess of 1000 vehicle accidents and incidents, as a trooper. Then, as a member of M.A.I.T. for 10 years, he was involved in over 1000 detailed investigations and collision reconstructions. Al has testified multiple times in state courts and he has been court qualified as an expert in accident investigation and collision reconstruction. Al’s work expertise focuses on investigating and reconstructing vehicle collisions involving single and multi-vehicles, animals, pedestrians, motorcycles, heavy trucks, and commercial vehicles. He is also a skilled user of forensic mapping technology and computerized collision diagramming software for collision scene analysis. Al is experienced in the data download and analysis of airbag black boxes (Crash Data Retrieval Units) in automobiles, pickup trucks, and SUVs. He holds a Bachelor of Science Degree in Political Science from Lander University in Greenwood, South Carolina and completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.

Burn Injury Involving Turkey Fryer

Product Design is Critical to Consumer Safety


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.  Read More

Retaining Wall Photo Carlos defect

When the Walls Come Tumbling Down… Retaining Wall Basics

A wall is really boring until it fails. A retaining wall is supposed to hold back soil to either support a structure or keep a space clear. When it fails, both of those roles are compromised. A retaining wall does not have to collapse to fail. In fact, a failure is perhaps better defined as when the wall does not perform as expected. Read More

Fire Place with Gas Logs

Stop or I’ll Soot!!!

Fire. Something about fire touches our brainstems…both good and bad!  Uncontrolled fire is terrifying and deadly to be sure.  But the controlled burning of wood at a campfire or in a fireplace in your home almost can’t be beat, to my mind! For that very reason, a fairly common amenity to houses nowadays is the gas log fireplace insert.

When not installed properly, these logs will generate soot. These soot particles can leave the fireplace and meander.  All. Over. Your. House.  Read More

a road crest at the top of as hill

Over the Hill


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? Read More

Machine guard for blog

Machine Guarding and Risk Assessment


The Occupational Health and Safety Administration (OSHA) “Top 10 for 2018” violations once again have Machine Safeguarding earning a position on the list. Machine safeguarding was the 9th most cited standard as noted in the list below:

  1. Fall protection, construction (29 CFR 1926.501)
  2. Hazard communication standard, general industry (29 CFR 1910.1200)
  3. Scaffolding, general requirements, construction (29 CFR 1926.451)
  4. Respiratory protection, general industry (29 CFR 1910.134)
  5. Control of hazardous energy (lockout/tagout), general industry (29 CFR 1910.147)
  6. Ladders, construction (29 CFR 1926.1053)]
  7. Powered industrial trucks, general industry (29 CFR 1910.178)
  8. Fall Protection–Training Requirements (29 CFR 1926.503
  9. Machinery and Machine Guarding, general requirements (29 CFR 1910.212)
  10. Eye and Face Protection (29 CFR 1926.102)


Read More

Placard location ALD

The Pressure to Keep Rolling (Part 2)


One of the first safety concerns for your vehicle should be your tires. The tires on your vehicle or trailer maintain contact with the roadway and assist you in getting to your destination safely. So how do you know that your tires are proper for your vehicle, are being well maintained, and beyond the obvious threat of tire failure, why is this important to know? Read More

Unguarded Shear point 1 white

Unguarded Shear Point on Force Tester Amputates Worker’s Finger

A worker was injured while testing gas springs similar to the type that hold the hatchback of an SUV open. The hazard that injured the worker was an unguarded shear point. The tester contained a mounting plate that was raised and lowered by a pneumatic cylinder.

The pneumatic cylinder lowered the mounting plate while the worker’s fingers were in the hazardous, unguarded shear point. Read More

Electric Hazard Guardrail photo

Hazards Can Lurk Anywhere … Watch Your Step …


While on a lunch stop during a recent vacation trip through Tennessee, I happened across a safety hazard that required immediate attention.  The establishment had a raised concrete patio at the front with a steel railing around the perimeter.  At one edge of the patio was a set of stairs with a continuation of the steel railing used as a handrail.  The top edge of the patio had light strings wrapping the top metal bar as accent lighting for the perimeter.  The light string continued down the stair handrail wrapped in the same manner as the rest of the patio. Read More

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