In the late 1880s, a young boy was electrocuted when he accidentally touched an unlabeled, energized telegraph wire. That incident ignited an inventor by the name of Harold Pitney Brown to make an impassioned plea in a New York Post editorial to limit telegraph transmissions to what he considered a safer level of 300 Volts.
Perhaps Harold thought that limiting electrical transmissions to levels of 300 Volts or less would provide instant electrical safety. With over 120 years of hindsight, we view things much differently today. Yet, Harold stumbled across two important concepts. The notion of "300 Volts" is a technical discussion about the laws of electrical energy (Ohm's Law, etc) that lends understanding to how electrical energy can kill or maim. On the other hand, the term "safe" reflects a working knowledge of the fundamental principles of safety. Our challenge is to combine our technical understanding of electricity with the principles of safety to ensure electrical safety is both practical and effective. The better we understand both concepts the greater the likelihood we will have to improve the status quo. The Risk Control Hierarchy (RCH) does an excellent job of blending these two key concepts.
Risk Control Hierarchy
The heartbeat of safety is the Risk Control Hierarchy (RCH), which is found in Appendix G of the ANSI Z10 Standard. The RCH helps us prioritize safety initiatives from least effective to most effective. For example, will you be safer wearing a helmet while riding a motorcycle or selling it all together? Selling the motorcycle eliminates the risk of an accident while wearing a helmet offers protection to your head from the risk of a head injury during an accident. The RCH works by helping us rank risk reduction measures from most effective to least effective as per below:
1.) Eliminating the risk.
2.) Substituting a lesser risk.
3.) Engineering around risk.
4.) Awareness of every risk.
5.) Administrate and regulate behaviour around risk.
6.) Protect workers while exposed to risk.
Note that each step above is equally important, yet not equally effective in protecting workers. Eliminating a risk is the most effective way to keep workers safe while protection from risk by using Personal Protection Equipment (PPE) is the least effective. There have been great improvements in the design of PPE, but its primary purpose is keeping workers alive - not 100% safe.
Safety and Risk
Risk, which is defined as exposure to a hazard, is two-pronged. Exposure and severity are probable for potential injury. For example, a 120V outlet is a greater risk than a 13.8KV switchgear line-up because more people are exposed to the 120V outlet. Since risk is exposure to hazards, then safety is the reduction and management of risk. The management responsibility of an electrical safety program typically falls to an electrical engineer because he or she understands electricity. In our modern world, we can never eliminate risk but are very good at finding new ways to reduce risk.
Another way to look at risk is the chart (Figure 2) developed by Ray Jones which shows the relationship between the worker and the safety infrastructure above him. A worker performing tasks must make many complex and specific decisions that affect his safety. In the case of electrical safety, energy isolation is very personal for electricians facing deadly electrical energy every time they open a panel. By the time they touch electricity, it's too late.
Zero Energy Verification--Is There Voltage?
Electrical accidents are impossible without electrical energy. If an electrician comes into direct contact with electrical energy, there is a 5% fatality rate. Shocks and burns comprise the remaining 95%. The NFPA 70e is very specific on how to isolate electrical energy. First, all voltage sources must be located and labelled. Multiple voltage sources are commonplace today due to the proliferation of backup generators and UPSs. Next, voltage test tag sydney devices must be validated using the LIVE-DEAD-LIVE procedure. Additionally, the voltage tester must also physically contact the voltage and must verify each phase voltage to the ground.
The RCH and Electrical Safety
How does the RCH apply to electrical safety?
1. Elimination -Removing all electrical energy exposure.
2. Substitution -Lowering the electrical energy exposure.
3. Engineering Controls -Reinventing ways to control electrical energy exposure.
4. Awareness -Revealing and labelling all sources of electrical energy.
5. Administrative Controls -Regulations that teach personnel safety around electrical energy.
6. Personal Protection -Reducing risks of working on live voltage.
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