Hurricane and Tropical Storm strength wind forces can wreak havoc on wood-framed residential structures. One of the primary hazards is the negative pressures which can develop on the exterior building envelope when the structure is subjected to the high encircling winds. These negative pressures act like the suction of a giant vacuum on a dwelling’s roof diaphragm, which produces enormous uplift forces throughout the entire structure. The leeward walls are also subjected to negative pressures, while the windward walls take the brunt of the positive wind pressures. The uplift on the roof is caused by what the author dubs “the airplane wing effect”. In other words, (more…)
This is a case study about an incident I investigated involving a major upset in a distillation column. This blog builds on the previous blogs about the Distributed Control System, DCS – Data is the Key
Distillation is a method of separating mixtures of compounds with differing boiling points. Uncle Bill with his still on the hill separates ethanol, that boils at 173°F, from water that boils at 212°F. If the mixture is heated to above 173°F, but below 212°F, the ethanol will boil, the vapor will travel up out of the unit and then can be condensed and served over ice with an olive… Any mixture of two or more chemicals with different boiling points can be separated in this way. The distillation (more…)
Surge Protective Devices (SPD), formerly known as Transient Voltage Surge Suppressors (TVSS) have been around for a long time. The most recognized version is integrated into outlet strips and used to protect sensitive electronics from surges, or higher than expected voltages on the power line. Early versions of these surge strips were known to have problems where internal components could overheat and cause a fire. Thermal protection was added to the designs to greatly reduce the potential for a fire hazard. Such an implementation in an outlet strip is considered a Type 3 SPD. (more…)
HVAC systems are almost everywhere in the United States now. As a life-long resident of the humid south that grew up in a home without central air conditioning; I definitely appreciate the ability of a well-designed and maintained HVAC system to remove the oppressive summer humidity.
The very humidity that makes your clothes damp with sweat and hastened the invention of cooled leather seats in automobiles also has another route to create havoc…condensate.
In order for an HVAC or “air-conditioning system” to reduce the humidity in the air of your home or office it must first cool the air down to a point where the air can no longer keep the moisture in suspension as water vapor. The moisture must condense… creating condensate. This is what is happening when your cool beverage of choice “sweats” on the exterior of the container in the humid summer. Now that you have liquid water, as opposed to water vapor, this condensate must be directed out of your conditioned space to prevent water damage due to backed up or leaking condensate. (more…)
The Kraft paper process was invented in 1879 and produces a stronger finished product that other paper manufacturing methods. One of the waste streams is known as black liquor and is a mixture of solids and water. It contains lignin, hemicelluloses and chemicals used in the pulping process. The original process had no use for this harmful waste stream and it was dumped into nearby waterways, to their detriment!!! Mr. G.H. Tomlinson invented the recovery boiler in the early 1930’s. This development made the Kraft process the manufacturing method of choice, as explained below. (more…)
From corrosion to site drainage, coastal regions present a host of unique and challenging issues for homebuilders and residential property owners alike. In this article, issues specific to coastal residential foundation installation and in-service function will be addressed. “Coastal residential” will refer to single-family homes within AE or VE tidal flood zones for the purposes herein. These locations typically exist in areas with close proximity to saltmarsh or beachfront, or on barrier sea islands. Per FEMA, in AE zones, the elevation of the first finished floor must be above the flood elevation for the building site. In VE zones, the elevation of the lowest horizontal structural member must be above the flood elevation for the site. Most building jurisdictions also require a minimum of (1) foot of freeboard, or additional space, between the flood elevation and these building features. As a result of these requirements, coastal residential structures must be supported by either crawl-space or elevated “drive-under” style foundations. It should be noted that wall-type foundations are prohibited in VE zones, and structures within these zones are required to be supported by monolithic elements such as columns, piers, or piles. Slab-on-grade type foundations are not permitted in flood zones where the foundation will exist within the flood plain. (more…)
According to published weather data for the year 2019, 2.35 billion lightning strikes were recorded across the world, with 223 million of these in the United States. The movement of atmosphere causes electrical charges to build up between clouds. A tipping point is reached where the insulating properties of the air cannot withstand the level of energy and a discharge occurs.
Image Credit: Charleston Post and Courier. A lightning strike over Charleston, SC on July 3, 2019.
A lot of people own motorcycle(s). Not a lot of people have experience riding motorcycles. More people have motorcycles stored in their garages, covered with all kinds of things, than ride motorcycles. In a similar neglect, there are those people who take their motorcycle out occasionally but never really put the miles or hours on the bike. This means that most of the people that have registered motorcycles do not get a lot of “seat time”. This issue leads to collisions involving motorcycles that should not have happened for more than one reason. When it comes to collision reconstruction and investigations, “ride to live” takes on a whole different meaning. (more…)
The fire service affords you the opportunity to witness and observe things that a lot of engineers and even most people do not get the chance to see. An example of this is the situation where extended elevated temperatures combined with poor construction techniques to result in a structure fire.
I have personally observed several occasions where a structure fire was initiated due to improper construction of the fireplace hearth extension. The most recent one followed a multi-day cold snap, at least by South Carolina standards. The thermometer read 17 degrees F as I drove to the call of smoke in a residence (more…)
Not too long back, I was on the scene of a collision case where a roadway defect was blamed for the loss of control that led to a single vehicle collision which resulted in major damages and serious injury. The collision was several years old, and the roadway had not changed over the time passed. My assignment was to inspect the roadway in the area of the crash, document it (by photographs and 3D scanning), and identify if there was a roadway issue that potentially led to the loss of control. What happened next was the result of going to the collision location and looking for more than what was to be expected. These things can help the case tremendously and make a huge difference in resolution. (more…)