Electrical Safety, Arc-Flash Hazard, Switching Practices, and Precautions (part 3)

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__4 Electrical Safety Practices and Precautions

The methods and techniques discussed in this section are industry accepted practices for working in or around energized electric power lines and circuits, and should be used only as guidelines. National and local codes and rules and regulatory standards should always take precedence over the guidelines discussed in this section.

The following rules are basic to electrical accident prevention:

Know the work to be done and how to do it.

Review working area for hazards of environment or facility design that may exist in addition to those directly associated with the assigned work objective.

Wear flame-retardant coveralls and safety glasses plus other recommended protective devices/equipment. Refer to the PPE categories specified under arc-flash hazard analysis for a specified task.

Isolate (de-energize) the circuits and/or equipment to be worked.

Lock out and tag all power sources and circuits to and from the equipment/circuit to be worked on.

Test with two pretested testing devices for the presence of electrical energy on circuits and/or equipment (both primary and secondary) while wearing electrical protective gloves.

Ground all sides of the work area with protective grounds applied with hot sticks. All grounds must be visible at all times to those in the work area.

Enclose the work area with tape barrier.

__4.1 Electrical Safety

The following general guidelines are provided on on-site safety, work area control, lock-out and/or tagging, protective apparel, testing of energized circuits and equipment, rubber gloves, voltage testers and detectors, grounds, circuit breaker maintenance safety checklist, and entering confined spaces. These guidelines should be supplemented as required to meet the applicable codes and regulations including the PPE required per arc-flash hazard analysis.

__4.2 "On-Site" Electrical Safety

Prior to going on an "on-site" electrical assignment, each worker should receive the following rules and should review and abide by them while on the assignment.

A foreman or qualified employee should be designated for each on-site assignment to provide on-site work direction and safety coordination. All personnel assigned to on-site electrical work should comply with the following directions:

Know the work content and work sequence, especially all safety measures.

Know the proper tools and instruments required for the work, that they have the full capability of safely performing the work, and that they are in good repair and/or are calibrated.

Check to determine that all de-energized circuits and equipment are locked out and that grounds are placed on all sides of the work area prior to beginning work.

Segregate all work areas with barriers or tapes, confine all your activities to these areas, and prevent unauthorized access to the area.

Insure that all energized circuits and equipment adjacent to the work area are isolated, protected, or marked by at least two methods (e.g., rubber mats, tapes, signs, etc.) for personnel protection.

Do not perform work on energized circuits and equipment without the direct authorization of your unit manager. When work on energized circuits and equipment has been authorized, use appropriate PPE required for the task, safety-tested equipment (i.e., rubber gloves, sleeves, mats, insulated tools, etc.).

Your foreman and qualified employee must inform you of all changes in work conditions. You then must repeat this information to your foreman and qualified employee to insure your recognition and understanding of the condition.

Do not work alone; work with another worker or employee at all times. Do not enter an energized area without direct permission from your foreman and qualified employee.

Discuss each step of your work with your foreman and qualified employee before it is begun.

Do not directly touch an unconscious fellow worker since he or she may be in contact with an energized circuit and equipment. Use an insulated device to remove him or her from the suspect area.

Do not perform, or continue to perform, any work when you are in doubt about the safety procedure to be followed, the condition of the equipment, or any potential hazards. Perform this work only after you have obtained directions from your foreman and qualified employee.

Do not work on, or adjacent to, any energized circuits and equipment unless you feel alert and are in good health.

__4.3 "On-Site" Safety Kit

The following are recommended protective tools to be used in preparation for and in the performance of on-site electrical work:

Red safety tape (300 ft) • Red flashing hazard lights (6) •

Safety cones (6)

Red "Do Not Operate" tags (15) • Padlocks, keys, and lock shackle (6) • Ground fault circuit interrupter-15 A, 125 V (1) • Fire extinguishers (2)

PPE

Flame-retardant coveralls

Safety glasses

Face shields

Hard hats

Other items required for protection on the job

Combustible gas/oxygen detectors

Portable ventilation blower

Ground loop impedance tester, ohmmeter (1)

Voltage detectors

Statiscope

1. Station type (1)

2. Overhead extension type (1)

Audio

1. Tic Tracer

2. ESP Voltage/ampere meter (1)

Amprobe

Simpson Rubber gloves and protectors of appropriate class

Grounding clamps, cables

Hot sticks

__4.4 Work Area Control

When workers are setting up the control area, it should be standard procedure that the safety coordinator be present and provide the required information.

Tape-solid red: A red tape barrier (with safety cones and red flashing lights) must be used to enclose an area in which personnel will be working. Other persons may not enter the isolated area unless they are actively working in conjunction with the personnel on the assigned work.

The purpose of the solid red tape barrier is to enclose and isolate an area in which a hazard might exist for individuals unfamiliar with the equipment enclosed. The only persons permitted within the solid red barrier are individuals knowledgeable in the use and operation of the enclosed equipment.

For their safety, workers shall not interest themselves in nor enter any area not enclosed by the red tape barrier except for a defined route to enter and leave the site.

It is important that the tape barrier is strictly controlled and the restrictions regarding its use are enforced.

When any workers are using solid red tape to enclose an area, the following requirements must be satisfied:

Place the tape so that it completely encloses the area or equipment where the hazard exists.

Place the tape so that it is readily visible from all avenues of approach and at such a level that it forms an effective barrier.

Be certain that the area enclosed by the tape is large enough to give adequate clearance between the hazard and any personnel working in the tape enclosed area.

Arrange the tape so any test equipment for the setup can be operated safely from outside the enclosed area.

Use the tape to prevent the area from being entered by persons unfamiliar with the work and associated hazards. Do not use the tape for any other purpose.

Remove the tape when the hazard no longer exists and the work is completed.

It shall be standard procedure that the workers should consider all areas out side the red barrier work area as energized and undertake no investigation unless accompanied by a knowledgeable plant employee.

Tape-white with a red stripe: White tape with a red stripe is used to enclose and isolate a temporary hazard (mechanical or electrical). No one is to enter this enclosed area. Obviously, if the enclosing of a hazardous area with tape is to be protective, the use of the tape barrier should be controlled and the restrictions on entering the area strictly enforced.

When any personnel are using white tape with a red stripe, the following requirements must be satisfied:

Place the tape so that it completely encloses the area or equipment where the hazard exists.

Place the tape so that it is readily visible from all avenues of approach and at such a level that it forms an effective barrier.

Be certain that the area enclosed is large enough to give adequate clearance between the hazard and any personnel outside the enclosed area.

Arrange the tape so that the test equipment for the setup can be operated outside the enclosed area.

Use the tape only to isolate a temporary mechanical or electrical hazard; do not use the tape for any other purpose.

Consider a striped tape area similar to an interlocked enclosure and treat as such.

Remove the tape when the hazard no longer exists.

__4.5 Lock-Out and/or Tagging

For the protection of personnel working on electrical conductor and/or equipment, locks must be placed on all open isolation devices designed to receive them. "DANGER" tags signed by the foreman or qualified employee must also be placed on the open isolation device.

Danger Tags: Danger tags may be applied only by authorized personnel and the tags must be dated and signed by the person applying the tag.

The following requirements must be satisfied when danger tags are used:

Danger tags are to be used only for personnel protection when the personnel are required to work on or near equipment that, if operated, might cause injury.

Danger tags are attached to primary disconnecting devices as a means of locking out equipment. Tag each source of power to the equipment and associated feeds (instrumentation circuits, PT's, CT's, etc.) to the equipment which is to be locked out.

Danger tags should be left on the equipment only while the personnel are working on the equipment or when a hazard to the personnel exists. A device bearing a danger tag must not be operated at any time ( FIG. 4).

Out of order tags: Out of order tags are used to restrict the operation of equipment which has a mechanical defect or for other reasons that are not related to the safety of personnel. Complete information concerning the reasons for the tag and a list of all persons authorized to operate the tagged device must be written on the tag ( FIG. 5).

Out of service tags: Out of service tags are used to indicate equipment that has been taken out of service. It is a white tag with letters on a black background.


FIG. 4 A sample of danger tag


FIG. 5 A sample of out of service tag.


FIG. 6 A sample of Gang lock clips to lock out equipment.

Caution tags: Caution tags are used to indicate potential hazard or unsafe conditions. These are yellow tags with yellow letters on a black background.

Use of danger tags: Danger tags are authorized for use on any isolation device as a method of locking out equipment. These tags must be hung so there is no doubt as to which device they control. The tags may be used and signed only by authorized personnel, who are designated by the plant manager.

When more than one crew or trade is working on the same equipment, each crew must attach its own tag and place its own lock on the device. Gang lock clips can be used as shown in FIG. 6 to provide maximum protection to a number of crews working on the same equipment or conductors.

Danger tags may be removed only by the person who originally placed and signed the tag. If that person is absolutely unable to remove the tag, a committee selected by the plant manager will fully investigate the situation.

This committee will remove the tag only when they are satisfied that they have full knowledge of the intention of the original tagger and that the tag may be removed without endangering anyone.

__4.6 Protective Apparel-Operating Electrical Equipment

All personnel must wear the PPE, i.e., apparel based on the arc-flash hazard categories required by NFPA 70E and OSHA regulations (see Sections 2 and 3) when working on electrical equipment which is, or might be considered, energized, or become energized as a result of the work. Following is a partial list of protective clothing covered in the PPE categories described in NFPA 70E:

Non-melting, flammable materials (i.e., untreated cotton, wool, rayon, or silk, or blends of these materials) with a fabric weight at least 4.5 oz/ydz FR shirt and FR pants or FR coverall

Cotton underwear-conventional short sleeve and brief/shorts, plus FR shirt and FR pants

Cotton underwear plus FR shirt and FR pants plus FR coverall, or cotton underwear plus two FR coveralls

Cotton underwear plus FR shirt and FR pants plus multilayer flash suit (3 or more)

Fire-resistant coveralls buttoned fully at the throat and wrists

Electrical lineman's safety gloves with protectors

A face shield which also provides forehead and hair protection, or a face shield which can be attached to a hard hat

All personnel shall wear protective apparel when withdrawing and inserting circuit breakers, connecting and disconnecting ground connections, and testing for energized circuits and/or equipment

Only qualified personnel shall be allowed to operate switching equipment

__4.7 Testing of Electrical Circuits and/or Equipment

General: All circuits and equipment are to be considered as energized until proven de-energized by testing with voltage detectors, and grounding cables are connected. The voltage detectors selected should be for the class of voltage supplied to the circuits and equipment to be serviced.

Personnel assigned to on-site electrical service work should be supplied with at least two electrical voltage detectors. The voltage detectors provided shall be capable of safely detecting the voltage present in the circuits and/or equipment to be serviced. The assigned personnel shall be instructed in the correct operation of each detector before each on-site electrical job.

Each electrical circuit and/or piece of equipment to be serviced should be tested by an assigned craftsman with two detectors and then tested by one other person who has been trained in the correct operation of the voltage detectors. This testing shall be performed in the assigned craftsman's presence to insure that the electrical circuit and/or equipment is de-energized.

The voltage detectors should be checked for proper operation immediately prior to and immediately after testing the electrical circuits and/or equipment to be serviced. These checks should be made on a known source of energized voltage, such as on the spark plug of a running automobile engine with a glow stick, or with a specifically designed tester supplied by the detector vendor.

While testing circuits and/or equipment, the craftsman performing the tests shall wear lineman's safety rubber gloves designed for the class of voltage in the circuits and/or equipment to be serviced and other protective equipment for this work.

Capacitors: A capacitor to be serviced must be removed from operation in the following sequence:

Isolate the capacitors by opening the breakers or isolation devices connecting them to the electrical system.

Permit the capacitors to drain off the accumulated charge for 5-10 min.

(There is generally a built-in device which accomplishes this drain.) Short circuit and ground the capacitors in the manner and with the protective equipment noted in section 4.11 (below). While performing these procedures, be very careful that sufficient distance is maintained from the capacitors with a hot stick in the event the drain-off device is not properly functioning.

Vacuum circuit breaker high-potential testing (hipotting)-cautions: Although the procedure for hipotting a vacuum circuit breaker is similar to that used for any other electrical device, there are two areas that require the exercise of extra caution.

During any hipotting operation, the main shield inside the interrupter can acquire an electrical charge that usually will be retained even after the hipot voltage is removed. This shield is attached to the midband ring of the insulating envelope. A grounding stick should always be used to discharge the ring as well as the other metal parts of the assembly before touching the interrupter, connections, or breaker studs.

High voltage (HV) applied across open gaps in a vacuum can produce hazardous X-radiation if the voltage across the contacts exceeds a certain level for a given contact gap. Therefore, do not make hipot tests on an open breaker at voltages higher than the recommended 36 kV alternating current (AC) across each interrupter. During the hipot test, the steel front panel and partial side panels should be assembled to the breaker. Personnel should stand in front of the breaker to take advantage of the shielding afforded by the panels. If this position is not practical, equivalent protection can be pro vided by limiting personnel exposure to testing four three-phase breakers per hour with the personnel not closer than 3 m (9 ft 10 in.) to the interrupters.

During equipment operation in the normal current carrying mode, there is no X-radiation because there are no open contacts.

Electrostatic coupling: When personnel are working on a de-energized circuit that is adjacent to an energized circuit, it is important to be certain that solid grounds are attached to the de-energized circuit at all times. A substantial voltage charge can be generated in a de-energized circuit by electromagnetic coupling with the energized circuit. The solid grounds will drain off this voltage charge.

__4.8 Rubber Gloves for Electrical Work-Use and Care

Rubber gloves with leather protectors that have been tested to at least 10,000 V must be worn when work is performed on or within reach of energized conductors and/or equipment. The rubber gloves and protectors of the appropriate class should be available to all trained personnel as part of the safety kit for on-site electrical work.

The rubber gloves and protectors are of two types:

1. Low-voltage rubber gloves and protectors (Class 0). These gloves are tested and approved for work on equipment energized at 750 V or less. (Permission should be given by the foreman for the use of low voltage gloves when working on conductors and/or equipment energized below 750 V.)

2. HV rubber gloves and protectors. The gloves are tested at 10,000 V (Class 1) for use on 5 kV or less, tested for 15,000 V for use on 10 kV or less (Class 2), and at 20,000 V (Class 3) for use on 15 kV or less voltage ratings.

Both HV and low-voltage rubber gloves are of the gauntlet type and are avail able in various sizes. To get the best possible protection from rubber gloves, and to keep them in a serviceable condition as long as possible, here are a few general rules that apply whenever they are used in electrical work:

Always wear leather protectors over your gloves. Any direct contact of a rubber glove with sharp or pointed objects may cut, snag, or puncture the glove and rob you of the protection you are depending on.

Always wear rubber gloves right side out (serial number and size to the outside). Turning gloves inside out places a stress on the preformed rubber.

Always keep the gauntlets up. Rolling them down sacrifices a valuable area of protection.

Always inspect and give a field air test (described later) to your gloves before using them. Check the inside of the protectors for any bit of metal or short pieces of wire that may have fallen in them.

Always store gloves where they cannot come into contact with sharp or pointed tools that may cut or puncture them.

All gloves are to be inspected before use. HV rubber gloves:

These gloves must be tested before they are issued. All gloves should be issued in matched pairs in a sealed carton. If received with the seal broken, return them for testing.

When HV gloves are issued to individuals for use over a three month period, they shall be inspected and tested at least every three months by a certified testing laboratory. All gloves, must be tested when returned to the tool crib after the job is completed.

Low-voltage rubber gloves:

Low-voltage rubber gloves must be inspected (see inspection of rubber gloves) before each use Defective gloves, or gloves in a questionable condition, must be immediately replaced Leather protector gloves:

Approved leather protectors must be worn over rubber gloves to protect them from mechanical injury Protectors that have been soaked with oil should never be used over rubber gloves Protectors that are serviceable for use over rubber gloves are not to be used as work gloves Protectors should be replaced if they have faulty or worn stitching, holes, cuts, abrasions, or if for any other reason, they no longer protect the rubber gloves Inspection of rubber gloves (all classes): Before rubber gloves are used, a visual inspection and an air test should be made at least once every day and at any other time deemed necessary during the progress of the job.

Visual inspection: When inspecting rubber gloves in the field, stretch a small area at a time (see FIG. 7), checking to be sure that no defects exist, such as (1) embedded foreign material, (2) deep scratches, (3) pin holes or punctures, (4) snags, or (5) cuts. In addition, look for signs of deterioration caused by oil, tar, grease, insulating compounds, or any other substance which may be injurious to rubber. Inspect the entire glove thoroughly, including the gauntlet.

Gloves that are found to be defective should not be mutilated in the field but should be tagged with a yellow tag and turned in for proper disposal.

Air test: After visually inspecting the glove, other defects may be observed by applying the air test as follows:


FIG. 7 Inspecting rubber gloves in the field.


FIG. 8 Testing a glove for air leak in the field-step 1.


FIG. 9 Testing a glove for air leak in the field-step 2.


FIG. 10 Testing a glove for air leak in the field-step 3.

Hold the glove with thumbs and forefingers as illustrated in FIG. 8.

Twirl the glove around quickly to fill with air ( FIG. 9).

Trap the air by squeezing the gauntlet with one hand. Use the other hand to squeeze the palm, fingers, and thumb in looking for weaknesses and defects ( FIG. 10).

Hold the glove to the face to detect air leakage or hold it to the ear and listen for escaping air.

__4.9 Low-Voltage Tester

This tester may be used for measuring AC or direct current (DC) voltage from 110 to 600 V when accuracy is not required. It can be used to test for continuity, blown fuses, grounded side of a circuit or a motor, and polarity.

This tester operates on the principle that the current passed through the solenoid of the instrument is proportional to the voltage under test and will cause the tester solenoid plunger to move in the same proportion. A pointer attached to the plunger indicates the voltage on the tester scale. This instrument has no internal protection: therefore, extreme caution must be used at all times.

Some models have a two-part neon bulb. Both parts glow when energized by AC. Only the part that is connected to the negative side of a circuit will glow when energized by DC.

When the low-voltage tester is used

Wear rubber gloves with protectors

Check the operation of the tester by testing a known energized circuit.

Assure good contact with the tester probes across the circuit being tested.

Read the voltage on the tester.

Because the low-voltage tester is designed for intermittent use only, continuous operation might burn out the solenoid, especially on the higher voltage.

Tic tracer (an audio voltage detector): The tic tracer is an audio voltage detector, which detects the electrostatic field surrounding an energized AC circuit and/or equipment.

This detector will operate only on unshielded AC circuits and/or equipment. It will detect the presence of voltages ranging from approximately 40 up to 600 V when hand held; higher voltages when used with approved hot sticks.

Wear HV rubber gloves and leather protectors when using the tic tracer to test circuits and/or equipment to be serviced.

Turn on the actuating switch on the side of the tic tracer.

Check the tracer by bringing it close to a conductor known to be energized.

Check for proper tracer operation by placing it near a lighted fluorescent bulb or at any known energized conductor of AC voltage.

__4.10 Medium- and HV-Detectors

Proximity Type: The proximity type HV tester is an instrument intended for use in detecting the electrostatic field surrounding an electrical conductor that is energized with AC at high potential. It is used only on AC circuits and/or equipment. The lowest voltage that can be reliably detected by this device is about 2000 V. Most detectors of this type have hard rubber or plastic tubular cases with one end for testing and a handle at the other end. A neon tube is used for voltage detection. There are several designs in various lengths for use in different situations. When the test end is brought near an uninsulated conductor that has been energized with AC at high potential, the neon tube will light with a red glow. A conductor that is surrounded by grounded metal has its electrostatic field effectively limited by the grounded metal; therefore, care should be taken that a conductor under test is not shielded in such a way as to interfere with the operation of the detector.


FIG. 11 Proximity type HV detector with neon tube.


FIG. 12 Proximity Type HV detector with periscope.

Use of a proximity HV detector

Wear HV rubber gloves of the appropriate class with protectors.

Wipe detector clean and dry. Check detector by bringing the test end close to an uninsulated conductor known to be energized at HV. Or you can use portable tester ( FIG. 11) by placing the lamp-end metal terminal of the detector against the testing point of the tester and pulling the trigger. If neon bulb of the detector glows, it is in good condition.

To test an uninsulated conductor to determine whether or not it is energized, bring the test end of the detector close to the conductor.

A red glow from the neon tube indicates that the conductor is energized. If there is no red glow from the neon tube, recheck the detector as explained above to make certain that the instrument is properly functioning.

In using the detector, turn the neon tube away from the direct rays of strong light in order to make the red glow from the tube more visible.

Wear rubber gloves and leather protectors when making tests with HV detectors and keep hands in back of guards on handles.

The proper type of detector, having sufficient length or extension, should be used to maintain proper body clearances for the particular voltage being tested. Some detectors are equipped with a periscope ( FIG. 12) so that the glow from the neon tubes will be visible from a greater distance. Care must be exercised in the use of the periscope type so the guard or hand does not block the line of sight.

Direct contact type: The direct contact type HV detector is an instrument intended for use in detecting the presence of an AC voltage with respect to ground by direct contact between the detector and the energized conductor.

It is used only on AC circuits and/or equipment. The lowest voltage that can be reliably detected by this instrument is about 2400 V to ground. The actual detection is normally done by a neon tube connected to one side of a forked contact terminal. The bulb is illuminated by a very small current flow due to the capacitance between an internal electrode and ground. This type of detector should not be used on ungrounded systems.

A special type phasing detector with two HV wands should be used if the system is ungrounded. These two wands are each touched to a different phase and the neon indicator detects phase-to-phase voltage. This device can also be used on grounded systems. The lowest voltage that can be reliably detected by this device is about 2000 V.

Important points to remember:

Assume all circuits to be energized until proven otherwise.

All protective equipment is to be proof tested for the voltage being worked.

Maintain all leads, probes, clips, and terminals in good condition.

Repair or replace defective leads.

Wear HV rubber gloves of the appropriate class with protectors.

__4.11 Grounds-Personnel Protection

Grounding is installed to provide a metallic connection from ground to de-energized circuit and/or equipment to be serviced. This is for the purpose of draining off static and induced electricity but, most importantly, to protect the worker, in the event that the equipment becomes accidentally energized. Before grounds are attached, the cable, bus, or equipment must be de-energized, isolated, locked out, and tagged. It must then be definitely established that the equipment to be grounded is de-energized by testing the circuits and/or equipment with voltage detectors.

The selection of the ground clamps is based on both the configuration and the electrical capacity according to the type of equipment to be grounded.

The ground cable is to be a flexible insulated copper conductor. The rules for sizing the ground cables to be used as protective grounds are:

The minimum size of cable to be used is a No. 1/0 American wire gauge (AWG) conductor.

The size of ground cables to be used must be at least equal to the size of the conductors feeding the circuit and/or equipment to be serviced. When the size of the ground cables or clusters is too large due to the system capacity, then bus sections or similar conducting materials must be used.

The cross-sectional area of the shorting paths and to ground must be sufficient to carry the short-circuit current. One or several conductors in a cluster may function as the grounding cable to carry the current. (A 4/0 AWG neoprene-insulated welding cable will pass 30,000 A for 0.5 s without melting the insulation.)

When installing ground clamps on electrical circuits and/or equipment, all workers shall use hot sticks rated for the voltage being worked. Several types of hot sticks, 6 to 8 ft in length, are listed as follows:

  • Rotary blade-universal end
  • Two-prong-universal end
  • Fixed blade-universal end
  • Rotary prong-universal end

While grounds are applied, the following protective equipment must be worn:

  • Flame retardant coveralls
  • Safety glasses
  • Electrical lineman's gloves with leather protectors
  • Hard hat
  • Face shield

In applying grounds, perform the following steps in sequence:

Attach the protective ground cable to the station or building ground grid.

If a ground system is not available, drive ground rods of sufficient cross section and number to carry the fault c

urrent. Be positive that a solid ground connection is made.

Test the value of the impedance of the ground cable and clamps with an ohm meter. The value should be much less than 10. Unless this value is extremely low, the ground connection is not adequate for personnel protection.

Connect one ground cable to the closest phase of the system and connect each succeeding phase in order of closeness. When removing the grounds, reverse the order so the application or removal of a ground will not require the crossing of an ungrounded-system phase. The grounds are applied to phases A, B, and C, in that order and removed in the reverse order.

Connect grounds to each phase of the circuit and/or equipment.

Check to determine that all connected ground cables are visible at all times when work is being performed.

Install grounds on all sides of the work area.

Switchgear ground and test (G&T) device: A G&T device is an auxiliary device, used with metal clad switchgear to ground equipment or to permit various tests, when equipment is out of service. The G&T device resembles a circuit breaker but is not designed to interrupt a circuit.

Switchgear "dummy" element: A dummy element is a device to provide a current path through a breaker compartment. The element frame resembles a breaker. The element is not designed to interrupt a circuit.

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