Photo by: @freetousesoundscom – Unsplash
Street lights are found everywhere from quiet neighborhood streets to the bustling downtown core. As we rely on this infrastructure to illuminate our streets, it is fair to say that public perceptions of streetlights are merely a docile component that serves one purpose: to generate light when it gets dark. Over the years, however, these systems have experienced controversy and criticism due to faulty electrical protection and insufficient supervision.
The dangers of contact voltage
One of the most prominent cases was the tragic death of Jodie Lane at Columbia University in New York on January 16th, 2004. Jodie walked over an electrified metal plate that had been flush with the asphalt while walking her dogs. The electrical danger was due to exposed wiring below the plate which combined with road salt and slushy snow conditions. This created a dangerous hazard capable of serious harm or death.
British Columbia is not exempt from these infrastructure flaws, having witnessed a similar incident in the Lower Mainland. In December 2016, a man was shocked by coming in contact with another electrified metal plate on a sidewalk in Burnaby. The man sustained no serious injuries but the faulty street light wiring and wet conditions were considered the root cause of this potentially fatal hazard.
Exploring these examples, we can highlight a universal problem with an aging electrical infrastructure that resides in the public domain. Both of these cases outline a situation where a conductive component became energized due to a fault scenario. Usually, electrical protection circuits protect against these events but in these particular systems, the protective circuitry is either inoperable or non-existent. These dangerous electrical conditions need to be monitored and mitigated to reduce the overall risk to the general public.
Defining voltage hazards
The Institute of Electrical and Electronics Engineers (IEEE) defines two terms to describe these types of hazards which are stray voltage and contact voltage. Both of these terms relate to the unwanted voltage that is present between two conductive surfaces that can be accessed by humans or animals. However, the difference between these two can be found in the root cause of the voltage hazard.
- Stray Voltage – A voltage resulting from the normal delivery or use of electricity that may be present between two conductive surfaces that can be simultaneously contacted by members of the general public or animals. Stray voltage is not related to electrical faults.
- Contact Voltage – A voltage resulting from electrical faults that may be present between two conductive surfaces that can be simultaneously contacted by members of the general public or animals. Contact voltage can exist at levels that may be hazardous.
To summarize, stray voltage results from normal delivery or use of electricity, whereas contact voltage is a result of an electrical fault. Contact voltage has been the culprit in many cases which often becomes a targeted focus for mitigation strategies due to its preventable nature.
Mitigation through heat maps
Photo: Hedgehog Tech generated heat map.
The associated risk from a hazard can be measured through the potential harm severity and the probability of the hazardous event occurring. In the case of street lighting poles, documented history outlines a significant degree of harm severity from electric shock in these systems. As described in the previous section The dangers of contact voltage, associated events with these system deficiencies can range from non-life threatening to fatal.
The probability of risk surrounding these systems can be attributed to the exposure to people, the occurrence of a hazardous event, and the probability of hazard avoidance. Understanding the current landscape of street lighting poles is critical in predicting the probability of an event:
- What is the age disparity between installations?
- What kind of system monitoring or protection methods are in place?
- Which pole locations correlate with higher pedestrian traffic?
- At what time of day are the systems energized?
These are questions that need to be investigated and documented in order to grapple with the task of quantifying the surrounding risk factors. This quantification can lead to the development of a vulnerability or “heat” map to provide dynamic context to the issue. These maps are an effective communication tool for illustrating the problem at hand through a risk heat grade based on collected data and project-specific calculations. They also provide visual evidence on how to stage the implementation of risk mitigation measures based on the highest risk prioritization.
This visualized data is important for the engineer to holistically understand the problem before designing a specific solution to address the concerns. When it comes to safer infrastructure, having clear and outlined data will support decision-making to reduce the risk factor.