Forensic Engineers and Consultants

Archive: Industrial

Why Pedestrians Overestimate Their Visibility: A Dive into the Psychology of Road Safety

When we step out onto the road as pedestrians, most of us assume that we are easily visible to oncoming drivers. However, research shows that pedestrians frequently overestimate their visibility, especially at night or in low-light conditions. This overconfidence can lead to dangerous situations, contributing to accidents and fatalities. Understanding why pedestrians overestimate their visibility is crucial for improving road safety and preventing accidents.

Pedestrians tend to believe that they are more visible to drivers than they actually are.

Because pedestrians can see the headlights of oncoming traffic and assume they are within the driver’s line of sight, they often mistakenly believe drivers can see them just as clearly. This bias may prevent pedestrians from considering the limitations of a driver’s view, such as blind spots, obstructions, or poor lighting conditions.

From the pedestrian’s point of view, vehicle headlights are extremely conspicuous. This may lead pedestrians to believe they are more visible to driver than they actually are.

In addition, pedestrians often assume that drivers are always alert and actively looking for pedestrians, particularly in areas with heavy foot traffic or near crosswalks. They might think drivers are always prepared to stop, even when the reality is that drivers may be distracted, focused on other traffic, or simply unable to see them in time.

Pedestrians might think that wearing light-colored or even dark clothing makes them sufficiently visible to drivers. However, research shows that at night or in low-light conditions, clothing without reflective materials is often not visible until it is too late. While light-colored clothing (like white or yellow) may offer slightly better visibility than dark clothing in low-light situations, it still falls far short of what is needed for drivers to see pedestrians from a safe distance. Research shows that pedestrians wearing light colors like white or yellow are not visible to drivers until they are dangerously close, especially at night. Dark clothing (such as black or navy) makes pedestrians nearly invisible to drivers at night. Dark clothed pedestrians blend into the background, making it extremely difficult for drivers to detect them in time to avoid an accident. Clothing with retroreflective material is far more effective in enhancing pedestrian visibility because the material reflects the light from vehicle headlights directly back to the driver. Research demonstrates that pedestrians wearing reflective vests, strips, or accessories are visible to drivers from much greater and safer distances.

Clothing with retroreflective material enhances pedestrian visibility at night.  Image credit Google Images.

The consequences of pedestrians overestimating their visibility can be severe. Thousands of pedestrians are injured or killed each year due to road accidents, with a significant number of these incidents occurring at night or in low-light conditions. Overconfidence leads pedestrians to take unnecessary risks, such as crossing roads without looking properly or assuming drivers will see them and yield.

Pedestrians overestimate their visibility due to biases, lack of awareness, and misconceptions about driver behavior. This overconfidence can lead to dangerous situations on the road. By understanding the psychological factors at play and taking proactive steps to increase visibility, both pedestrians and drivers can contribute to safer roads and fewer accidents. Road awareness is the first step toward reducing risks and improving both pedestrian and driver safety.

Ellen Szubski, Ph.D., CXLT, CPSI, AHFP, is a human factors consultant at The Warren Group. She earned a Doctorate of Philosophy in Human Factors Psychology and a Master of Science in Applied Psychology from Clemson University.  She did her dissertation on “The Influence of Pedestrian Biological Motion on Time-To-Collision Estimates at Night”.  She is also a Certified XL Tribometrist, Certified Playground Safety Inspector and a Certified Associate Human Factors Professional (AHFP). Prior to entering the forensic field, Ellen planned and conducted experiments for a major bicycle manufacturer. She also conducted laser strike perception studies for the Department of Defense.  Ellen applies her experience in Human Factors to the analysis of crash investigations and other personal injury matters. These matters often include collisions involving vulnerable road users and drivers, driver distraction, and slips, trips, and falls. She utilizes her knowledge of OSHA regulations, codes, and standards in her analysis of premises liability incidents and safety consulting.  Ellen is a current member of the Human Factors and Ergonomics Society (HFES) and it’s Forensic Professional Technical Group.

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Human Factors and Halloween Hazards: Trip and Falls

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Trick-or-treating is a fun and festive activity, but it comes with certain hazards that can pose risks to children and even adults. In addition to vehicle and pedestrian collisions and accidents, tripping and falling while trick-or-treating is a common hazard, especially for children navigating unfamiliar and dimly lit areas at night.

Children and adults can face tripping hazards on walkways while trick-or-treating.

Tripping hazards can be mitigated through compliance with walkway safety standards such as ASTM F 1637-2021: Standard Practice for Safe Walking Surfaces. ASTM F1637 is a standard that provides guidelines for the safe design, construction, and maintenance of pedestrian walkways to help prevent slip, trip, and fall incidents. In general, this standard emphasizes the importance of maintaining both interior and exterior walkways in a condition free of hazards such as protrusions, holes, and other tripping risks.

While trick or treating, elevation changes are a potential tripping hazard for children and adults. According to the safety standard ASTM F1637-21, vertical elevation changes up to ¼ inches are allowed in walkways. Vertical elevation changes between ¼ and ½ inches must have a beveled edge with a slope no greater than 1:2 (rise:run). Any vertical elevation changes greater than ½ must be transitioned by either a ramp or stairway that complies with applicable building codes, regulations, standards, or ordinances, or all of these.

Elevation changes on the sidewalk pose a tripping hazard for trick-or-treaters during Halloween.

In addition to elevation changes in the walkway, illumination plays a significant role in preventing trips and falls during trick-or-treating. Walkways should be properly illuminated to ensure visibility and safety, particularly in areas with changes in elevation or potential hazards. ASTM F1637-21 states that minimum walkway illumination must comply with local codes and ordinances. If local codes and ordinances do not address walkway illumination, then the recommendations set forth by the Illuminating Engineering Society of North America (IES) shall be used. 

Tripping can be a common hazard while trick-or-treating. Ensuring that elevation changes and illumination comply with safety standards such as the ASTM F1637-21 can help prevent children and adults from suffering a trip and fall while trick-or-treating and contributing to a safer environment for all pedestrians.

Ellen Szubski, Ph.D., CXLT, CPSI, AHFP, is a human factors consultant at The Warren Group. She earned a Doctorate of Philosophy in Human Factors Psychology and a Master of Science in Applied Psychology from Clemson University.  She did her dissertation on “The Influence of Pedestrian Biological Motion on Time-To-Collision Estimates at Night”.  She is also a Certified XL Tribometrist, Certified Playground Safety Inspector and a Certified Associate Human Factors Professional (AHFP). Prior to entering the forensic field, Ellen planned and conducted experiments for a major bicycle manufacturer. She also conducted laser strike perception studies for the Department of Defense.  Ellen applies her experience in Human Factors to the analysis of crash investigations and other personal injury matters. These matters often include collisions involving vulnerable road users and drivers, driver distraction, and slips, trips, and falls. She utilizes her knowledge of OSHA regulations, codes, and standards in her analysis of premises liability incidents and safety consulting.  Ellen is a current member of the Human Factors and Ergonomics Society (HFES) and it’s Forensic Professional Technical Group.

Human Factors and Halloween Hazards: Vehicle/Pedestrian Collisions

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Trick-or-treating is a fun and festive activity, but it comes with certain hazards that can pose risks to children and even adults. In addition to trip and fall hazards while trick-or-treating, there is also an increased risk of vehicle/pedestrian collisions due to the increased pedestrian activity in the roadway at night.

Child trick or treating during Halloween in the roadway.

At night, there are two significant problems facing drivers that contribute to pedestrian/vehicle collisions: the degraded visual abilities of drivers and the low contrast of pedestrians. The human visual system is severely limited at night. Both the visual ability to recognize objects and see fine detail, and the ability to recognize low contrast objects like pedestrians are diminished at night. In night, humans experience a loss of color perception and hue as well. Drivers are typically unaware of the extent to which their visual abilities are reduced at night, as suggested by the selective degradation theory which states that a driver’s ability to detect and recognize roadway hazards degrades with lower illumination, while their ability to steer the vehicle remains unchanged. The unchanged ability of a driver to maneuver a vehicle allows the driver to remain confident in their nighttime driving skills, despite their severely degraded visual capabilities in detecting and recognizing roadway hazards like pedestrian trick-or-treaters during Halloween.

Drivers face two significant problems while driving at night: the degraded visual abilities of drivers and the low contrast of pedestrians.

In addition to the degraded visual abilities of drivers, the low contrast of pedestrians within a roadway environment is also a significant problem that contributes to pedestrian/vehicle collisions at night. At night, a driver has decreased sensitivity to fine details, color, and contrast, therefore they are less likely to detect and recognize pedestrians. Pedestrians can enhance their visibility to drivers by increasing their contrast through visibility aids such as retroreflective material. Pedestrians can be made more conspicuous to drivers through the proper placement of appropriate visibility aids. Conspicuity differs from visibility such that a conspicuous object is defined as one that ‘grabs’ the observer’s attention with minimal visual search and is easily recognizable. A visible object is defined as an object that simply contrasts with the background. The more conspicuous the pedestrian, the less likely a collision between the pedestrian and driver. (Please see my previous article titled “The Big Difference Between Conspicuity and Visibility” for more information on the distinction between visibility and conspicuity.). Trick or treater pedestrians should aim to increase their conspicuity with active lighting or retroreflective materials while in the roadway during Halloween in order to enhance their safety.

In conclusion, the degraded visual abilities of drivers and the low conspicuity of pedestrians on the road contribute to pedestrian vehicle collisions at night. During trick-or-treating for Halloween, there is increased pedestrian activity in the roadway at night, increasing the risk of vehicle/pedestrian collisions. Drivers are largely unaware of their diminished visual abilities at night and may overdrive their headlights. Pedestrians typically lack sufficient contrast within their environment to be visible and conspicuous to drivers. An awareness of a driver’s degraded visual abilities at night in addition to decreasing vehicle speeds and increasing the conspicuity of pedestrians may help decrease pedestrian/vehicle collisions at night during Halloween.

Ellen Szubski, Ph.D., CXLT, CPSI, AHFP, is a human factors consultant at The Warren Group. She earned a Doctorate of Philosophy in Human Factors Psychology and a Master of Science in Applied Psychology from Clemson University.  She did her dissertation on “The Influence of Pedestrian Biological Motion on Time-To-Collision Estimates at Night”.  She is also a Certified XL Tribometrist, Certified Playground Safety Inspector and a Certified Associate Human Factors Professional (AHFP). Prior to entering the forensic field, Ellen planned and conducted experiments for a major bicycle manufacturer. She also conducted laser strike perception studies for the Department of Defense.  Ellen applies her experience in Human Factors to the analysis of crash investigations and other personal injury matters. These matters often include collisions involving vulnerable road users and drivers, driver distraction, and slips, trips, and falls. She utilizes her knowledge of OSHA regulations, codes, and standards in her analysis of premises liability incidents and safety consulting.  Ellen is a current member of the Human Factors and Ergonomics Society (HFES) and it’s Forensic Professional Technical Group.

Materials in HVAC Plenums

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What materials are suitable for installation in Heating, Ventilation, and Air Conditioning (HVAC) plenums?  Let’s first define a plenum.  The 2021 edition of the International Mechanical Code (IMC), a subset of the International Building Code (IBC), defines a plenum as “an enclosed portion of a building structure, other than the occupied space being conditioned, that is designed to allow air movement, and thereby serve as a part of an air distribution system.”

Here we note that the occupied space is excluded from the definition, and the portion of the building structure that is designed to allow air movement is the focus.  This is the key to understanding when a space in a building can be considered a plenum.

Is a portion of the building structure, for example a space above a suspended ceiling or a mechanical room or closet, designed to allow the movement of air as part of an air distribution system?  If air moves through these spaces as opposed to through a duct system, then the space is a plenum.

Open return fan coil unit in a ceiling.

When a plenum is present, there are specific requirements in the code for the materials installed in a plenum.   Chapter 6 of the IMC section 602.2.1 Materials within plenums states as follows:

Except as required by Sections 602.2.1.1 through 602.2.1.8, materials within plenums shall be noncombustible or shall be listed and labeled as having a flame spread index of not more than 25 and a smoke developed index of not more than 50 when tested in accordance with ASTM E84 or UL 723.

       Exceptions:

  1. Rigid or flexible ducts and connectors shall confirm to Section 603.
  2. Duct coverings, linings, tape and connectors shall conform to Sections 603 and 604.
  3. This section shall not apply to materials exposed within plenums in one- and two-family dwellings.
  4. This section shall not apply to smoke detectors.
  5. Combustible materials fully enclosed within one of the following:
    • Continuous noncombustible raceways or enclosures.
    • Approved gypsum board assemblies.
    • Materials listed for and labeled for installation within a plenum and listed for the application.
  6. Materials in Group H, Division 5 fabrication areas and the areas above and below the fabrication area that share a common air recirculation path with the fabrication area.

The IMC requires that materials within a plenum be noncombustible or have a flame spread index of not more than 25 and a smoke developed index of not more than 50.   Why?  Since a plenum is part of the “air distribution system” any smoke or byproducts of combustion that are generated will be distributed throughout the area that is served by the plenum.  If the plenum is on the return of an air distribution system, then potentially all of the areas served by the respective supply system will receive any smoke that is generated if the system is running.  If the plenum were to be on the supply side of a system, then any smoke or byproducts of combustion will be distributed to the area served by the respective supply plenum.

Why does this matter?  The National Fire Protection Association (NFPA) tells us that most fire deaths are caused by smoke inhalation and not by actual burns.  As an interior structural firefighter and a fire investigator, I have seen this to be the truth.  The smoke will often get you before the flames do.  So as designers and installers of HVAC systems, we want to minimize the spread of smoke to the best of our abilities.

In my role as a forensic engineer, I often see materials that do not meet the requirements of the IMC regarding flame/smoke spread installed in plenum areas.  Big offenders are often PVC piping, data cabling and electrical wiring.

Often plenums are created by installing an open grille in the door or wall of a mechanical room and allowing the return air to pass through the mechanical room to the open return on the air handling unit.  This room is by definition a plenum and the requirements of the code with regard to flame/smoke spread apply to this space. Materials installed in this plenum must meet the flame spread of 25 and smoke developed of 50.  A repeat offender is the condensate drain line on an air handling unit.  PVC is not suitable or listed for use in a plenum.  Copper is a much better choice as it will not burn.  CPVC can also meet the flame/smoke spread requirements but check the listing to be sure.

Finally, don’t forget wires.  Most modern wiring and cabling will have some type of man-made insulation on it.  Be sure that all of these meet the flame/smoke spread requirements as well when installed in plenums.  Plenums are often found above ceilings in commercials structures where cabling and wiring are found as shown in the photograph with the hydronic fan coil unit.  Also, raised computer room/data center floors are often used for both routing of cables and supply or return of conditioning air.  Here all items installed in the plenum must be rated for this type of installation.

Example of plenum spaces

While plenums can be advantageous in the design and installation of a building HVAC system, they add a new layer of requirements that must not be ignored for the safety of the occupants of the building.

Chad Jones, PE, CFEI, CVFI, CMSE has a Bachelor of Science in Mechanical Engineering from Clemson University. Chad has over 25 years of engineering experience including mechanical, process, and manufacturing engineering. 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. A lifelong auto and motorcycle enthusiast, Chad is accomplished in the maintenance, repair, and modification of vehicles and engines. Chad is a Certified Fire and Explosion Investigator, Certified Vehicle Fire Investigator, and IFSAC certified Firefighter II in Greenwood County, South Carolina.

Dig into Underground Fire Water Piping and Appurtenances

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Many sites that are protected by fire sprinklers will have at least some amount of private underground fire water piping. Its purpose is to make water available for fire protection or suppression at a needed flow and pressure. Its presence is usually quietly evidenced by the connected objects that occasionally surface along its course, like valves, fire department connections and private hydrants, termed appurtenances. Underground water piping commands attention, though, when Read More

FORKLIFT Etiquette: DON’T BE A LOUSY TIPPER!

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That is always good advice to follow if you are a forklift driver!  Operating a forklift can be a dangerous occupation.  There are approximately 1 million forklifts (powered industrial trucks) in the US workplace today, and it is estimated that just over 10% of those are involved in some type of accident every year.  Forklift accidents result in dozens of deaths and thousands of non-fatal injuries annually.  About one out of every four of those accidents involves a tipping or overturning forklift, making this the most common type of industrial truck accident.  Read More

Understanding Heat Transfer: A Guide for Fire Investigators

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In the realm of fire investigation, understanding heat transfer is crucial. Heat transfer plays a significant role in how fires start, spread, and ultimately, how they can be analyzed and investigated. There are three primary modes of heat transfer: conduction, convection, and radiation. In this article, we’ll delve into each of these modes and explore examples of how fire investigators can apply this knowledge to their work. Read More

Dive Into Suction Tank Issues and Inspections

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Privately-owned water tanks supplying fire protection systems have a long history. The NFPA published the Standard on Gravity Tanks in 1909. It is one of the oldest NFPA codes, predating even the Life Safety Code’s precursor, the Building Exits Code, first published in 1927. The Standard on Gravity Tanks evolved over the years to become NFPA 22, Standard for Water Tanks for Private Fire Protection. The inspection, testing, and maintenance requirements for all types of private fire water storage tanks are laid out in NFPA 25, Chapter 9 – Water Storage Tanks. While there are about eight different types of fire water tanks, I’d assert that the most common type today is the steel suction tank. Read More

Civil Twilight Pedestrian Collision: A Case Study

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Susan, a 45-year-old runner, was jogging in the early morning approximately an hour before sunrise, also known as “civil twilight.” Civil twilight occurs both before sunrise and after sunset when the sun is below the horizon and the sky is partially illuminated. Susan was wearing dark athletic clothing and grey tennis shoes for her morning run. She was running on the sidewalk in a suburban area and began to cross the four-lane road at an unmarked crosswalk. Read More

Rainy Day Troubles: A Slip and Fall Case Study

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An afternoon summer rain shower led to an elderly woman’s admittance to the hospital. Mrs. Jones, aged 68, entered a retail store to buy groceries for her visiting family. Mrs. Jones walked through the store’s vestibule toward the entrance where she slipped and fell, sustaining significant injuries. An investigation was conducted to determine the cause of the slip and fall incident.

The investigation revealed Read More

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