Forensic Engineers and Consultants

Archive: Commercial

Don’t Get Burned With Your Gas Grill!

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.

I am quite familiar with safe gas grill design and use as, prior to entering the forensics field, I was the Vice President of Engineering at a gas grill manufacturer. Since then, in my practice as a forensic engineer and fire investigator, I have investigated many structural fires and burn injuries involving gas grills.  Typical incidents involve a fire at a grill that spreads to an adjacent residence or an operator that is burned during the use of the grill.  Figure 1 shows a grill which was involved in a residential fire. The grill was improperly installed too close to combustible wood supports. Figure 2 shows flames that issued from the operator’s access opening on a gas grill when it experienced a delayed ignition.  Excessive LP gas had accumulated in the grill due to a leaking valve.  The flames injured the grill’s operator.

Figure 1: Remains of a gas grill that was installed too close to combustible wood support framing. A fire started at the grill and spread to the adjacent residence.

Figure 2: Flames exiting from the operator’s access opening on an unlisted and improperly designed gas grill. The flames injured the grill’s user.

Generally, injuries and fires occur when proper procedures are not followed.  These procedures relate to the design, installation and use of the grills. Regarding the design of gas grills, there are several relevant product standards.  The primary standard is ANSI Z21.58 Standard for Outdoor Cooking Gas Appliances.  Larger gas grills are sometimes designed to ANSI Z83.11  Gas Food Service Equipment.  Additionally, equipment such as smokers or turkey fryers are covered under ANSI Z21.89 Outdoor Cooking Specialty Gas Appliances. I have designed and had products laboratory approved to each of these standards. The standards include many safety requirements of the product’s design and construction.  They also mandate many performance tests that the grill must be able to pass. Also specified are many of the required warnings and information to be supplied in an owner’s manual. Generally, mass produced gas grills have been designed to one of these standards and tested and listed by a testing lab such as UL, ETL or CSA.  “Listed” means included on the laboratory’s database of approved products.  This is a key step in ensuring a reasonably safe gas grill.  Many of the gas grill burn injury cases I have investigated involved unlisted gas grills.  These may lack the safe design provisions and proven performance of listed gas grills.

However, even listed gas grills can have problems if they are not installed in a correct manner.  Gas grills broadly fall into two categories, those with “self-contained” fuel supplies (like 20 pound LP tanks) or “fixed fuel” grill installations that are supplied with either natural gas service or LP gas from a larger fixed bulk tank.  These are illustrated in Figures 3 and 4. Each of these types has specific installation requirements.  For the self-contained fuel type with a normal LP cylinder, these installation requirements largely relate to following the manufacturer’s requirements as to the proper location and operation of the grill.  Additionally, there are code regulations regarding the use of such grills.  For example, gas grills with 20 pound LP cylinders cannot be used inside buildings and are generally not allowed to be used on balconies of apartment buildings.

Figure 3: Freestanding LP gas grill with “self-contained” fuel source, in this case a 20 pound LP cylinder.

Figure 4: Dual grills installed in one island enclosure. This style of installation is called a “permanent” installation with a “fixed fuel” supply. The grills shown were involved with a burn injury incident.

Grills that are permanently installed in a surround or island (see figure 4) and are supplied with fuel gas from a fixed fuel source have more involved code requirements.  Codes require that these grills be listed to either ANSI Z21.58 or ANSI Z83.11. Additionally, the installation must be in accordance with the manufacturer’s instructions.  In some locales, the construction of the grill island and installation of the grill will require an installation permit and inspection.   In addition to the installation of the grill, the fuel supply system itself, whether LP or natural gas, often will require an installation permit with inspection.  The fixed fuel supply system itself must be designed and installed per the requirements of the relevant gas code, typically either NFPA 54 National Fuel Gas Code, NFPA 58 Liquified Petroleum Gas Code and/or the International Fuel Gas Code.

Once the gas grill has been manufactured and installed in a proper manner, the user must operate the grill in an appropriate manner.  This generally requires operating and maintaining the grill in accordance with the manufacturer’s instructions. A common operational problem is the delayed ignition of accumulated fuel that creates a larger than normal fire which burns the operator.  Another problem that occurs is a fire at the grill that spreads to the surrounding structure.  Problems in the design, installation or operation of the grill may cause or contribute to these situations.

If you have a burn injury or fire incident that involves a gas grill, contact Warren for an informed investigation that will consider all the potential causes of the incident.


What You May Not Know About Using a Concrete Test Hammer

When assessing potential problems in concrete structures, consider a non-destructive test using the concrete test hammer, AKA “rebound hammer,” before investing a lot of time and money needlessly replacing or destructively testing the concrete structure.  The use of rebound hammer tests should be considered before you or your client decide to drill multiple core samples. Large areas of the concrete structure suspected of having potential strength problems can be tested quickly with a rebound hammer.  Analysis of those results can narrow down specific areas for more rigorous testing.

A rebound hammer consists of a spring-loaded steel hammer which, when released, strikes a steel plunger in contact with the concrete surface. The spring-loaded hammer must travel with a consistent and reproducible velocity. The rebound distance of the steel hammer from the steel plunger is measured on a scale attached to the frame of the instrument, giving you the Hr number.

Compressive strength versus rebound number

The rebound hammer test is used to assess the in-place uniformity of concrete, to delineate regions in a structure of poor quality or deteriorated concrete, and to estimate in-place strength development. The non-uniform area can become a target area for further testing. The further testing is used to establish the relationship between the rebound number and the compressive strength.

Rebound Hammer

For a given concrete mixture, the rebound number is affected by factors such as moisture content of the test surface, the method used to obtain the test surface (type of form material or type of finishing), and the depth of carbonation. These factors need to be considered in preparing the strength relationship and interpreting test results. To estimate strength in an existing structure, establish the relationship by correlating rebound numbers measured on the structure with the strengths of cores taken from specified locations.

Uniformity is not the same as strength. It should be noted that according to the American Concrete Institute (ACI) Provision of ACI 301-16, a rebound hammer cannot be directly used for in-place strength testing. However, this same provision allows use of a rebound hammer in accordance with ASTM C805/C805M, if specified by the Architect/Engineer, only “to evaluate uniformity of in-place concrete or to select areas to be cored.” At the same time, Provision states: “Results of in-place strength tests will be evaluated by Architect/Engineer and are valid only if tests are conducted using properly calibrated equipment in accordance with recognized standard procedures and an acceptable correlation between test results and concrete compressive strength is established and submitted.” However, no specific non-destructive testing methods or equipment for in-place strength evaluation are listed. For a review of in-place methods for estimating concrete strength, including the rebound hammer, refer to ACI 228.1R.

Drilling for core sample

Concrete specimen

This testing procedure might help avoid having to use ground penetrating radar and then drilling core samples for compressive strength tests. It is designed to provide data in the field on concrete structures without causing damage and gives an immediate indication of uniformity.  It is economical, quick, and simple to use.  Its results can be used to estimate compressive strength for the structure.  If you have concrete in question, consider the use of a rebound hammer test along with a thorough visual inspection as part of the first steps in the investigation of the structure.

Carlos Zarraga has more than 9 years of engineering experience in the structural field specializing in building design, building components and foundation design.  Carlos has designed and analyzed structures, supervised designers and drafters, prepared construction documents and provided on-site duties for field supervision and inspection of construction projects. Certified in RISA 3D, RISA Foundation and RISA Connection, he is well-versed in the analysis of foundation failures.   He often determines the root cause of failure and the resulting scope of damage.  He has designed retrofits to existing structures in addition to repairing construction defects.  He also has experience in the industrial and petrochemical industry designing structures for materials handling facilities and industrial buildings.  Carlos holds a Bachelor of Science in Civil Engineering from the University of New Orleans.

The Demise of Insulation on Electrical Wiring


Unlike fine wines and some types of cheeses, not everything ages well.  Such is the case with the materials used as insulation of electrical wiring.  While the copper metal used as the conductor in many wire types will last virtually forever, the cladding used to protect and insulate the wire allowing electrons to flow to their final destination does not. Read More

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


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. Read More

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


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 Read More

Construction Techniques to Prevent Water Penetration at Windows

Windows, and their interface with the exterior walls, are an important part of a building’s envelope that resists the intrusion of water. Most builders take many precautions to protect a house from water damage. One of the most important factors in keeping the water out is the installation of window flashing, a thin material that prevents water from seeping in around a window. Read More


Ammonia – The Good, The Bad, The Smelly… Part One

Ammonia is a compound consisting of one nitrogen atom and three hydrogen atoms and is denoted by the formula NH3. Its boiling point is -28°F at atmospheric pressure, so unless it is under pressure, it is gaseous at room temperatures. Therefore, pure ammonia is typically stored under pressure in a liquid form. Household ammonia is only 5-10% NH3, the remaining 90-95% is water. Ammonia is extremely soluble in water. It is often depicted  like this: Read More

The CE Mark and What Should It Mean to You? Part One


Two little letters, CE.  Perhaps you have seen those two letters on a machine nameplate or some other equipment.  What is the meaning behind those two stylized letters and how does it drive the design of safer machinery?  Let’s take a closer look. Read More

Hidden Heat: The Unseen Hazard of a High Resistance Connection


A typical residence can have upwards of 10,000 feet of electrical conductors installed, most of which are buried in the walls, attics and crawlspaces.  A commercial building can have 100,000 to upwards of 1 million feet of electrical conductors.  At each device such as a switch or a receptacle are at least three, and typically six or more connections of these conductors within a junction box.  The connections can be in the form of twisted connectors, screw terminals, push in terminals and crimped connectors.

Read More

Failure to Maintain Tow Hook Latch Results in Bystander Death


An unfortunate and tragic case that we investigated involved a commercial “rollback” recovery truck that was being used to transport a four-wheel drive diesel pickup.  The diesel pickup was not in running order with its’ engine in the bed of the truck.  Consequently, a commercial towing company was hired by the truck owner to transport the truck.  In the process of loading the truck onto the rollback, the truck came uncoupled from the winch and cable system.  The truck then rolled down the inclined bed of the rollback, running over and killing a bystander. Read More

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