Q: Can a boom truck be used as a manhole rescue device? I’ve heard that OSHA rules prohibit boom truck use because the truck has too much force, resulting in greater harm to the employee in need of rescue.
A: There may be issues with a boom truck as a rescue device, but its use is not prohibited in the situation you mention. Based on the criteria for rescue, however, it’s possible that the use of a boom truck may not be your best option. Incident Prevention does not advocate this method nor any other particular method of rescue from a manhole, but we do make every attempt to give you the information you need to make the right decision.
We often hear that OSHA requires a tripod and winch. That is usually because of the following statement OSHA made regarding manhole rescue in the original 29 CFR 1910.269 preamble: “The equipment must enable a rescuer to remove an injured employee from the enclosed space quickly and without injury to the rescuer or further harm to the fallen employee. A harness, a lifeline, and a self-supporting winch can normally be used in this manner.”
Your question creates an opportunity to better understand OSHA's role in workplace safety and the methodologies they employ in developing and enforcing standards. While OSHA uses the above preamble example as a method of accomplishing rescue, they never required the tripod and winch as the method to be employed for rescue from a manhole. If you are a regular reader, you know that Incident Prevention endeavors to deliver practical advice toward compliance. With few exceptions, the OSHA rules are a body of performance standards telling us what the employer must accomplish in order for the employer’s workplace to be considered safe, not how the employer must do it. Within those performance rules are the criteria for what must be accomplished.
The issue of using boom truck hoists for rescue has been raised many times. There are obvious risks that don't invalidate use of a hoist for rescue, but it depends on how you plan to use it and how you plan to mitigate the risks involved. One scenario may be to mount a rescue pulley to a boom tip, or another employer may plan to use the boom to lift an injured employee from a manhole. As pointed out in your question, the power of a hydraulic lift could cause additional injury if an injured employee were to strike the lip of the manhole during extraction. We have seen pulleys mounted on boom tips and capstans mounted on outriggers as the means of extraction. The method of rescue is up to the employer. The employer’s responsibility is clearly defined, including the requirement to practice and identify the issues with the selected method. When asked in the past about using a hook on a boom truck as a fall protection anchorage or as a rescue device, OSHA says it may not meet the requirements of the standard, usually referring to the requirement to do no further harm. If the employer can demonstrate that the risk is controlled, there is no issue.
Incident Prevention’s consultants have observed that tripods and winches are excellent rescue devices, but obviously they may have limitations, especially if there are more than two workers in a hole or if terrain around the manhole precludes setting up a tripod. In the latter case, before you resort to lifting using a boom truck, you may find manhole ring lip-mounted or bumper-mounted rescue booms that will work.
Q: Regarding substation fence signage, some signs in the marketplace read “Danger” while others read “Warning.” What is the proper terminology?
A: The proper terminology for a safety sign is based on the level of risk to the reader of the sign and where they are when they see it. We surveyed several of our editorial advisory board members and other utility safety people, as well as contractors who serve several utilities, and got different answers. Most common were “Danger” signs on fences and “Warning” signs on control room doors. Most of these sign usages are likely based on long-ago determinations of sign applications, and there are a variety of opinions regarding interpretation of the guiding ANSI Z535 standard. However, Incident Prevention has access to Allen L. Clapp, P.E., of Clapp Research, who not only sits on the Incident Prevention editorial advisory board, but also sat on the ANSI sign committee representing IEEE for 20 years and chaired the ANSI Z535.2 standards committee that established current criteria for facilities signs. This was also the beginning of the era when ANSI recognized and applied new research led by Clapp and Electromark that identified fundamental issues and improvements in recognition of sign meaning. Their work proved the greater hazard recognition provided by the new, now mandated rectangle key word and hazard statement signs used today, moving away from the older oval danger signs no longer allowed by the ANSI Z535 standard.
It is important to note here that OSHA standards are generally workplace related for the protection of workers, but OSHA also includes the public in the scope of the accident prevention sign standard. The ANSI sign standard applies to facilities as well as general environments, but is also to be employed to protect workers in the workplace. As with any workplace safety signs, there must be consistency in the signage, and employees must be trained to recognize sign meanings and associated actions no matter how the employer interprets sign application. The public does not get safety sign training. As such, ANSI sign standards are developed based on methodologies designed to trigger positive or protective reactions by members of the general public who see signs.
Both OSHA 1910.145 and ANSI Z535.2 have criteria for sign use. Each standard has slight but not irreconcilable differences. ANSI uses a three-tier sign system while OSHA uses a two-tier system based on the outmoded Z35 safety sign standards that were replaced by the Z535 standards. For ANSI, the differentiation between “Danger” and “Warning” is the space on either side of a line of demarcation such as a fence. A “Danger” sign is required on the side of the fence where the deadly hazard lies. A “Warning” sign is placed at the barrier to warn the reader that there is a hazard beyond the sign that will result in serious injury or death. If conditions could result in minor or moderate injury, a “Caution” sign is required. For OSHA 1910.145(c)(1) and (c)(2), a “Danger” sign is required if the conditions beyond the sign will result in immediate danger. If the conditions could result in potential hazards, or to caution against unsafe practices, a “Caution” sign is required. OSHA has no provision for “Warning” signs. The “Warning” signal word was first required by the 1991 Z535 standards that replaced the 1968 Z35 standard adopted by OSHA in 1972.
Both standards use the same warning colors with respect to the danger words. Red is used for “Danger,” yellow is used for “Caution” and orange is used for “Warning.”
Though the OSHA standard does not contain a provision for “Warning” signs, there is provision following the safety sign section for use of “Warning” tags. Rule 1910.145(f)(7) allows “Warning” tags to be used to represent a hazard level between “Caution” and “Danger,” instead of the required “Caution” tag, provided that they have a signal word of “Warning” and an appropriate major message regarding the hazard. OSHA has adopted ANSI Z535.2 in the adopted standards even though the rule as written in 1910.145 does not specify or even mention the use of a “Warning” safety sign.
Now that we have a better understanding of the rules, the guiding criteria for a substation fence sign is based on protection of the public. Using the ANSI criteria, a “Warning” sign would be appropriate. Inside the station, “Danger” signs are appropriate where workers and any nonauthorized members of the public are at risk. However, anyone climbing transformers or buss support structures, opening a hatch covering energized or rotating parts, or entering a barricaded area would be in the immediate area of the related hazards. As a result, signs at approaches to energized areas behind fence barricades, barriers or hatch covers generally need to use the “Danger” signal word (see NESC Rule 124C3) inside the station.
For more information about safety signs, see “NESC and ANSI Z535 Safety Sign Standards for Electric Utility Power Plants and Substations” by Allen L. Clapp, P.E., at http://incident-prevention.com/ip-articles/nesc-and-ansi-z535-safety-sign-standards-for-electric-utility-power-plants-and-substations.
Q: ASTM 712 says phase-to-phase rating only applies if both phases are covered. How does that apply to cover-up when a worker is positioned between phases? For example, the circuit is 7,200/12,470 volts. Would a Class 3 plastic cover-up – maximum use 15.3 kV phase to ground – be adequate for use if only one phase is covered?
A: According to the table and notes for ASTM F712.4, Class 3 plastic is rated 26.4 guarded phase to guarded phase and 15.3 kV guarded phase to ground. The answer to your second question is a definite maybe. It depends on several things, the most important of which might be practices employed by workers.
Look closely at the language of the 712 standard. First, 712 is a manufacturing standard. Paragraphs 1.3 to 1.5 read, “It is common practice for the user of this equipment to prepare instructions for the correct use and maintenance. The use and maintenance of this equipment is beyond the scope of these test methods. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.”
Now let's look at the notes to the 712 test tables. Plastic guards are tested phase to ground. In Table 1 and 2, the withstand and flashover tests, ASTM states that withstand ratings are tested at greater than the maximum phase-to-ground ratings, but they are not rated – meaning tested – for use on one uncovered phase to one guarded phase. Note 1 states, “Plastic guard equipment … is designed to provide a satisfactory safety factor only when used in a phase-to-ground exposure. If exposure is phase-to-phase, then a satisfactory safety factor is only provided if the exposure is covered-phase-to-covered-phase.” In other words, the testing assures a certain safety factor for phase-to-ground application because that is how it is tested.
To understand that, let’s spend a moment discussing safety factors. Plastic goods show a rating for phase to ground and a rating for guarded phase to guarded phase. You will read two numbers on rubber goods, one a maximum voltage use rating, the other the test voltage. For Class 2 rubber, the use rating is 18 kV and the test voltage is 20 kV. That shows a 2000-volt safety factor. Class 4 rubber is tested at 40 kV and use rated at 36 kV, showing a safety factor of 4 kV. There is no differentiation in rubber goods as to whether a voltage rating is phase to phase or phase to ground.
ASTM is explaining the standard practice for testing, not necessarily the practices for use. The application criteria for the employer is found in OSHA 1910.269(l), which simply requires insulated cover to protect employees, and paragraph 22.214.171.124 of IEEE 516, “IEEE Guide for Maintenance Methods on Energized Power Lines,” which states that when working within reach or extended reach, the equipment should be covered with protective cover-up equipment rated for the voltage involved. Neither OSHA nor 516 establishes an application of insulation based on safety factors, only insulation ratings.
As to the original question, in practical use it is common for employers to apply Class 3 plastic rated 15.3 kV guarded phase to ground to 12.4-kV primary as cover between phases if one phase being worked is not covered. An employee positioned between phases is able to reach between the electrical component of both phases, meeting OSHA's definition of multiphase or phase-to-phase exposure. A Class 4 rubber hose rated for use at 36 kV would be accepted as appropriate for covering one phase while the worker, using appropriate practices and in rubber gloves, is in contact with the uncovered phase. Most experts we talked to agree that a Class 3 plastic rated at 15.3 kV phase to ground would also be acceptable.
This is why we pointed out in the beginning that practices are important. As an industry, we generally forbid any contact with more than one phase at a time, even if they are covered. It is generally accepted, then, that a single covered phase on a 12,470-volt feeder with a plastic, rated at 15.3 kV covered phase to ground, combined with appropriate practice, would be effective protection for the worker.