Q: I understand OSHA has made a final announcement on minimum approach distances. Can you explain the latest information?
A: On December 22, 2016, OSHA issued a memorandum to regional administrators regarding the enforcement of minimum approach distance requirements in 29 CFR 1910.269 and 1926 Subpart V (see www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=31079). The memorandum had an effective date of July 1, 2017. Readers will recall that concerns about the rising risks of transient over-voltages were the basis for the increased minimum approach distances published by OSHA in 2014. The bottom line is that OSHA has accepted an industry engineering analysis – an IEEE paper titled “Practical Approaches to Reducing Transient Overvoltages Factors for Live Work” that was delivered at IEEE’s 2016 ESMO conference – as a basis for the final guidance of the memorandum. The guidance for enforcement is simple, but it is divided for above and below 72 kV. Following are the choices spelled out in the memorandum.
New Transient Table
The IEEE paper established a new Table A with standard transient multipliers based on voltage. The employer may still calculate their own minimum approach distances utilizing an engineering analysis approved by the standard using transients published in the new Table A.
New MAD Table Over 72 KV
OSHA has published a new Table B, derived from the agency’s 2014 published tables but calculated with the new IEEE Table A transient values. Employers may use Table B over 72 kV if they follow the notes to the table and if they meet a series of conditions designed to limit transients. The conditions are:
Below 72 KV
Below 72 kV, transients are no longer considered an issue and employers may use the legacy Table 6 in Appendix B to 1910.269. Table 6 is in line with both the IEEE and NESC tables published in their respective consensus standards.
Q: OSHA extended crane operator certification until November 2017, but we are still confused about the exemptions for utilities both for digger derricks and knuckle-booms. Can you help us understand those exemptions?
A: Yes, the exemptions have not changed. The digger-derrick exemption is pretty simple. If the operator is setting poles, performing work associated with setting poles or hanging equipment located on poles, the digger-derrick operator is exempt from holding a crane operator’s third-party-issued certification. We consider loading poles from a pole pile onto a pole trailer to be associated work. Setting padmount transformers also is specifically allowed by OSHA. Setting structure steel, setting reinforcing steel or setting apparatus in a substation is not covered under the exception.
Knuckle-booms are not an exception specific to utilities. The knuckle-boom exception is from OSHA’s cranes and derricks standard and applies to all knuckle-boom operations. The exemption was designed for delivery drivers who hauled and dropped bulk materials at a materials yard. The rule states bulk unloading is an exception, but placing for installation is not. For utilities, an example of the exception would be a knuckle-boom unloading a trailer-load of poles onto a pole pile. On the other hand, a trailer with a knuckle-boom that is being driven on a right-of-way and dropping poles at staked locations for setting would not be considered an exception. The operator would have to be a licensed crane operator.
Q: As we have developed our certifications for cranes, we have not been able to find the certification criteria for riggers. What are we missing?
A: You are not missing anything as there are no certification requirements for riggers. The requirements for riggers to be qualified are no different than for any other job in the workplace. All employees must be able to perform assigned tasks without endangering themselves or others. An unqualified person performing any task is a risk to themselves and others. The degree of qualification is based on the nature and degree of risk associated with the task. All employees must be qualified to perform their assigned tasks safely. Reading the preamble to OSHA’s cranes and derricks standard, it is clear that numerous incidents had occurred during the assembly of large cranes, and many of those incidents were a direct result of incompetence in the erection of cranes and in the assembly of components for rigging. In fact, the frequency of assembly failures and incidents was the driving force for the creation of the title assembly/disassembly (A/D) director, with a much more detailed listing of the qualifications and competencies for the A/D director, but no one has ever asked me about A/D director certification.
The quest by employers to certify riggers has largely been a misunderstanding of the written standards, clouded by offerings of training vendors. OSHA’s cranes and derricks standard does not require certification of riggers. There is one rule associated with riggers – 1926.1404(r)(1) – that states the employer must ensure the rigging work is done by a qualified rigger. That is the extent of the requirement. It is up to the employer to determine what qualifications the rigger must have to be qualified. Many employers choose to do training and issue a certification, but the OSHA standard does not require it.
Q: Our company safety rules require that we test grounds yearly. We have been sending them to a lab to certify the tests, but since we have increased the amount of grounding cable by 600 percent in the last six years, both the turnaround and expenses are becoming difficult to manage. Our management seems to think testing must be performed by a testing lab. Can you help us understand the rules?
A: Testing and inspection are critical to assuring that grounds perform as designed. Many companies, recognizing how important testing is, have adopted off-site testing, and over the years many people have assumed that a certified lab is required. That’s not the case.
OSHA does not dictate testing methods or intervals for testing grounds, nor have they adopted any of the referenced standards for testing of grounds. That means the guides we use from IEEE and ASTM are not mandatory, but using them as a guide is the right thing to do. OSHA does refer the employer to the IEEE and ASTM guides as references for information. There is some diligence and conscientious performance required to test grounds, but training and careful selection of personnel to do the testing is an effective and expedient way to keep grounds ready for use in the field.
There are several test units available on the market. Buyers should do their research to determine which will provide the test criteria they need. DC units perform a DC resistance test. DC is not subject to induction and reactance, so a ground being tested by DC can be left coiled during the test. Many experts feel an AC test may be a better indicator of how a cable will perform in the field because an AC test measures in total impedance. Users should carefully read manufacturers’ guides since an AC test can be affected by reactance from clamp spacing and cable arrangement. Results can even be affected by the metal tube on the interior of a plastic or PVC table, or steel reinforcing in concrete under the ground cable being tested.
Besides AC/DC, essentially there are two ways to test your grounds that are in practice by utilities. One is the low-current ohm value method; the other is the full-current method. Both provide necessary information on the integrity of the grounds, and the information derived should be calculated into the peculiarities of the system they will be used on. Many grounds testers using low-current values simply show a pass/fail result. In reality, if we know the test values and the available system fault values, we can calculate risk to the worker and develop procedures and methods to provide the best possible protection.
High-current testing produces a two-part result and is considered by many to be a preferred method. The full-current test impresses a current across the ground under test, usually up to 200 amps, and will stress any poor connections to a degree not possible in a low-current ohms-resistance test. Comparisons of the two methods regularly have shown current testing to reveal connection issues not revealed in a low-current ohms test. Earlier editions of IEEE 1048, “IEEE Guide for Protective Grounding of Power Lines,” had discussions of grounds testing, including a discussion of high-current testing values, but eliminated that section from the most recent edition. For testing, IEEE 1048 now refers the reader to ASTM F2249, which does not describe in detail the value or process for high-current testing. ASTM does, however, include section X2 – “Temperature Differential Test Method for In Service Testing of Copper Grounding Jumper Assemblies” – in the appendices to ASTM F2249-2015. The section describes how high-current tests use the heat stress imposed on the cable to proof-test the cable connections by thermal scanning after AC heating under load.
You will find AC full-current test discussion and procedures in IEEE 1048-2009 (the previous edition). Most high-current testing machines we are familiar with provide a graph associated with current rise and results in voltage drop calculated at maximum-rated fault current for the cable under test. Since voltage drop is critical in determining voltage across a lineworker, these readings often are preferred over knowing the impedance of a cable and following up with a calculation of voltage drop.
Do your research, select your test equipment in accordance with the needs of your system, and train your test operators to perform diligent and conscientious testing. It will pay off.
Q: We are using a testing machine for portable protective grounds that gives us a pass/fail result. Our concern is the pass/fail does not seem to line up with risk data we find in various consensus standards. Where do we go to sort this out?
A: The results from the test unit manufacturer are relative to the data they used in developing and programming their equipment. In practice, it is your own calculated variables, procedures and grounding schemes that determine realistic pass/fail criteria.
Here is an important concept: The calculations for pass/fail are relative to other parallel paths with the ground under test. If you use the value of 1,000 ohms for a man in parallel with the results of the cable under test, you can calculate the voltage and available current across the man based on the maximum current delivered. From there you can make other recommendations, such as doubling cables, establishing criteria for work boots and work gloves, and work methods that will decrease voltage drop or current across the lineworker, improving protection for the worker.
On the values, most grounds tester manufacturers use tables computed on conservative values for current and voltage hazard levels, so their fail indicators also are conservative. Most of the manufacturers also have a disclaimer in their instructions reminding the user it is their responsibility to establish the appropriate criteria. OSHA uses 50 volts and 50 mA as the hazard threshold, which are very conservative values also used by NFPA 70E and others. In reality, the voltage – considering the worker is in shoes and work gloves – can realistically be 100 volts or more and still not break the electrical resistance across the worker. In addition, the mass of the worker determines risk threshold, and that can be survivable at 200 mA depending on the exposure time and weight of the person exposed. By the way, Charles Dalziel’s work, the basis for risk thresholds, usually is represented as a simple table based on results of exposures during his tests. The whole of his research is available on the web and quite interesting to read.
Of course, if you build your protection around equipotential techniques, none of the above matters. If you accomplish equipotential or even near-equipotential, there is no voltage drop. If there is no voltage drop, there can be no current flow to endanger the worker. Still, grounds testing is important to ensure hidden defects won’t cause a ground to fuse or fail before the circuit trips and clears. The ground must be able to trip a circuit and withstand the current for the time required to be of any value, so testing is required, and integrity of grounds and application are key to surviving an incident in any scenario.
© 2004 - 2021 Incident Prevention™. All Rights Reserved.