Loading...

Risk Control Hierarchy Refines Electrical Safety

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 in 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 by selling it altogether? Obviously, 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 behavior 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 a risk by using Personal Protection Equipment (PPE) is 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. There is the probability of exposure and severity of 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 the 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 the 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 labeled. Multiple voltage sources are commonplace today due to the proliferation of back-up generators and UPS's. Next, voltage testing 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 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 labeling 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.

Electrical workers are exposed to the greatest risks at the lower levels of the RCH. Recognizing that these 'residual risks' are present; the NFPA 70e tells workers how to perform their work safely in spite of these risks. In fact a large portion of the NFPA 70e details how to best manage these risks through Awareness, Administration, and Personal Protection. On the other hand, the greatest opportunity for risk reduction comes by focusing in the upper part of the RCH. Huge improvements in electrical safety will come by Eliminating Substituting, and Engineering solutions that manage electrical energy exposure.
The Department of Energy (DOE)

For better insight into the RCH process, let's look at a 2005 Department of Energy report on their electrical safety record. This report cited six reasons for their 14.1 electrical incidents per month.
Within this DOE report, "hazard identification" [Table 1] stood out as an administrative control issue resulting in numerous electrical incidents. The solution was to get tougher administrators or look for improvements higher up in the RCH. Right above Administrative Controls (see Figure 1) we learn that increasing employee's awareness of electrical hazards will reduce these types of incidents. A potential solution is to label and mark all voltage sources (hazards) feeding the electrical system. Voltage indicators and voltage portals wired to each voltage source provides two benefits: It identifies the voltage source and provides a means to check the status of that voltage source without exposure to voltage. Apply the same process to "LO/TO violations".

CAUSES OF INCIDENTS PRESENT RCH PRINCIPLE INCREASED RISK REDUCTION RCH PRINCIPLE Lack of hazard identification.

ADMINISTRATIVE Properly administrating NFPA 70e requires all electrical enclosures to have warning labels with incident energy level (calories). AWARENESS /ELIMINATION Marking all energy sources on the panel exterior provides personnel with simple yet safe hazard identification.

LO/TO violations including shortcuts or lack of energy verification

ADMINISTRATIVE Can the LO/TO procedure be rewritten to reduce exposure to voltage?

ELIMINATION /SUBSTITUTION Thru-door voltage pre-checking 'eliminates' all exposure to voltage for mechanical LO/TO* and provide significant risk reduction for Electrical LO/TO.

Reducing electrical energy to Cat 0/1 will greatly reduce the potential arc flash energy SUBSTITUTION Lowering the arc flash energy effectively 'substitutes' for a lower risk for a higher risk.

Elimination: The Hall of Fame of Safety

We can enter the Electrical Safety Hall of Fame by finding ways to eliminate voltage exposure. Here are a few practical examples that can be implemented today:
o Mechanical Lock-out Tag-out [LOTO]: LOTO procedures requiring electricians to verify zero energy before performing mechanical maintenance needlessly exposes workers to voltage. Since all voltages do not create mechanical motion, through-door voltage checking devices as part of a mechanical LOTO procedure will eliminate voltage exposure (see Appendix B).
o Why open a control panel? What maintenance functions can be moved to the outside of the panel? Thru-door data access ports are becoming commonplace because they allow programming with the panel door closed (Figure 3). A more recent example is an unmanaged Ethernet switch mounted outside the panel. This unique device allows full through-door access for a worker to troubleshoot and reset the Ethernet switch (Figure 4). What other devices can be re-engineered around through-door electrical safety? Perhaps putting certain branch circuit breakers on the outside of the panel is a good application?
o Control Panel Design: Provide a physical separation between the power and control compartments within an enclosure may become a standard. Voltages under 50 volts are considered safe, so reducing the control power to 24VDC makes the control power section safe to work on while it is energized.
These above examples are only 'scratching the surface', so I challenge you to find ways to eliminate voltage exposure.

Conclusion

When safety works perfectly, nothing happens! When there is an incident or a close call the RCH should be an inspiration to find a better way. By applying the RCH principles to electrical safety risks, it will open our eyes to see more practical ways to reduce those risks. Perhaps, we would expend more resources finding electrical safety solutions that will provide both higher safety and productivity dividends.

Harold Pitney Brown intuitively knew that eliminating risks would save lives. He just got one detail wrong when he thought that 300 Volts was not a risk. Now for the rest of the story: To prove that AC voltage is more lethal than DC, Thomas Edison hired Harold Pitney Brown to develop the first electric chair that executed William Kemmler on August 6, 1890. So much for electrical safety!



Article Source: http://EzineArticles.com/3679965

Belum ada Komentar untuk "Risk Control Hierarchy Refines Electrical Safety"

Posting Komentar

Iklan Tengah Artikel 1

Loading...
Loading...
Loading...

Iklan Bawah Artikel

Loading...
Loading...