Can a High Voltage Shock Ruin Hardware

Prepared past Matthew Jasica, March 3rd, 2017

What is High Voltage?

"High voltage" is a relatively arbitrary term, used to refer to electric energy large enough to crusade harm to humans. Diverse agencies and organizations have their own definition.
The International Electrotechnical Commission adopted the following thresholds:

• > thousand V_rms for Air conditioning power
• > 1500 5 for DC power

These may refer to either the potential difference betwixt a high voltage platform and ground or two conducting surfaces of a system. Discover that this does not make whatever reference to the electric current or total stored energy in the organization…

Where tin nosotros find high voltage in the lab?

• Power supplies and ability cables
• Capacitor banks
• Certain batteries
• Any electrically conductive surfaces energized by the above

High Voltage Hazards

General Electrical Hazards

Electrical Stupor/ electrocution
Electric shock occurs when sufficient electrical current is able to travel between two conductive surfaces through the body. This typically occurs between an energized surface and the ground simply can occur betwixt any two potentials. The risk and severity of the shock depends on a combination of  the voltage, current, and frequency (AC or DC.)
Depression voltage does not necessarily mean low take chances.

Electric shock may crusade burns, damage to muscles, nervous system, and internal tissue damage. Put in context:

• five mA is enough to induce reflexive action loss of muscular control. In Air-conditioning systems this tin can prevent the victim from being able to let get of an energized surface.
• 75 mA can cause ventricular fibrillation of the middle (a rapid, ineffective heartbeat) and, ultimately, death
• 100 J is enough to stop (or get-go) a heart.
• one thousand J can blow of entire body parts

Guidelines:

• The conventionally accepted electric shock risk thresholds are l 5_rms and 5 mA.ⁱ
• Whatever current above 10 A, regardless of voltage, should be treated as a take a chance^two
• Stored free energy (e.m. in a capacitor bank) greater than 10 Joules should be treated every bit a gamble²

Because a potential deviation is required for current to catamenia, information technology is possible with the proper equipment to isolate oneself from the ground (or any other potentials) and perform operations on energized platforms. This is only recommended for highly-trained professionals and does not completely eliminate risk of electrocution.

Burns and fire hazards

Pushing current through any not-superconducting cloth creates rut. Burns may occur either as a event of skin harm electric shock or due to the conductor being resistively heated to damaging temperatures. Please refer to our pages on fire safety and high-temperature condom for more details.

High voltage operations may as well present burn hazards:

• Inappropriate equipment for the needed current may become hot plenty to melt or combust nearby material.
• The stored energy in a spark or arc may be sufficient to ignite combustible (or explosive) fabric.

High Voltage-Specific Hazards

Explosion hazards

Stored energy of 10 J or more (or at conditions of V > 250 or I > 500 A) may create arcs, sustained discharges of electricity between conductive surfaces through a dielectric medium (e.chiliad. air). As higher up, this may be sufficient to ignite flammable or explosive cloth. This is specially important if combustible gasses are employed in the arrangement.

X-ray hazards

Electrons accelerated to energies of 20 keV, as in many vacuum systems, create x-rays (10-rays may exist created at lower energies, but are typically sufficiently-shielded by the housing equipment.) Boosted shielding may be required. For more than information see the page on radiation condom (in progress.)

Field Effects

Electric fields associated with high voltage may consequence in electrical breakdown, complimentary movement of accuse through a dielectric medium (ordinarily air). Unlike in an arc, accuse does non need to stop at a 2d conductive surface. The discharge created by a tesla coil is one example of electric breakup. This consequence is enhanced at abrupt surfaces, such equally un-rounded corners or points. As with the to a higher place, this may present shock, burn, burn, and explosive hazards.

Dielectric breakdown of air past a tesla coil. Image from Wikipediaⁱⁱⁱ

Personal Protective Equipment

Depending on the application, the following PPE may be advisable:

• Fire-resistant clothing
• Insulated boots  (OSHA 1910.136)
• Insulating gloves, mats, and blankets (OSHA 1910.137, OSHA 1926.97)
• Hot stick: Electrically insulated stick (typically fiberglass) with a tool on the end employed for various operations, including testing for high voltage, intentionally grounding conductive surfaces, and even performing certain mechanical operations, depending on the tool.

Chart of insulating glove ratings from JM Test Systems, based on OSHA 1926.97 Tables E-1 and E-two⁴

Laboratory Best Practices

HV Safety Design (and Operation) Rules

The following is taken from a paper by D.C. Fairchild on high voltage and loftier voltage safety for the CERN particle accelerator school:

The almost fallible role of any arrangement is the person operating it. High-voltage safety systems must be design to make them idiot-proof. For regular use it is not acceptable to take safety reliant on an operator correctly following a procedure… It is important that the system is designed in such a way that makes it impossible for an absent operator to hurt themselves or others."⁵

Faircloth lays out the following 4 loftier voltage blueprint safe rules:

1. Impossible for to accidentally lock someone in the HV area. In large facilities, this is typically implemented in the form of a "search" system, where the operator must physically disengage diverse locks and buttons in unlike regions of the HV area before the HV system can exist engaged.
2. Power to close down the ability inside and outside the HV expanse (such every bit an emergency-cease button.)
3. Impossible to power on the HV without locking the area. Interlock switches connected to gates and keys.
4. Incommunicable to enter the HV expanse without making it safe. If admission to the HV surface area occurs, all HV platforms should exist forcibly grounded. This is particularly important when sizeable capacitors are involved. But considering it's not actively energized does non mean it is safe!

Equipment

The post-obit is applicative to both high and low-voltage systems.

• Just use equipment (cables, terminals, etc.) that is rated for your anticipated usage. Check an amperage chart for what wire gauge is appropriate for your arrangement. (Wikipedia currently maintains a chart based on NFPA 70E.) Bear in mind that these conditions may alter with the organization environment.
• Fuses, breakers, resistors, and Ground Mistake Circuit Interrupters (GCFI) should be used to limit the current through a circuit.
• Regularly inspect cables carrying high voltage for holes, tears, punctures, cuts, or texture changes that may indicate deterioration. Immediately replace any damaged equipment.
• High voltage cables are heavy. Utilize proper supports and strain relief.
• Characterization or mark energized surfaces (fifty-fifty with color-coded tags) this includes labeling of grounded surfaces, when appropriate.
• Use proper insulation to isolate energized equipment and terminals. This may be solid (insulating blocks or shields),  liquid (oil–even vegetable oil suffices in a pinch), or gas (SF_{half dozen}).
  • Know the breakup abiding of whatever insulating medium and maintain enough distance between surfaces at different potentials to prevent arcs. For air this is roughly xxx kV/cm

Personnel and Facility management

• High voltage areas, enclosures, boxes, and cabinets should be labeled with proper signage in accordance with OSHA 1910.
  • Equipment at 50 V or greater should be isolated from people and labeled with a warning sign
  • Equipment at 600 Five or greater should exist in complete, insulated, secure, and marked enclosures
• Keep loftier voltage areas dry and weatherproof.
• Limit access to high voltage areas and operation of high voltage equipment to those with proper training. Multiple tiers of limited or restricted access should exist employed when appropriate.
• Maintain a Standard Operating Process for all high voltage equipment, specially if multiple users are involved. A checklist is particularly helpful, as even the most experienced users can make mistakes or overlook something.
• Loftier voltage workers should be trained in both CPR and AED utilize
• Know the location of the nearest AED (frequently in building hallways near labs)

Fire Safety

While fire safety is more extensively covered on another page, certain practices relevant to electrical safety listed by UW EHS Burn down & Life Safety are summarized hither:

• Eliminate use of extension cords, wherever possible. Restrict to temporary usage.
• Never plug an extension cord into a a relocatable power tap (eastward.g. power strip)
• Protect whatever relocatable ability taps from environmental hazards (such as fall hazards)
• Proceed a minimum of 36″ clearance for access to electrical panels (in accordance with Fire Code)
• Maintain a clear path of egress. The go out route should be labeled and visible, fifty-fifty following a loss of power.

First Assist

Burns and burn-related first aid and emergency response take been covered elsewhere. This department will focus on first aid for victims of electrocution.

• When you first see a potential victim of electrocution:
  • Bank check for a response without approaching the victim. Your own safety is your first priority. If the source is energized when you touch is, y'all tin can besides become a victim!
    
  • Prevent access to the chancy surface area
  • Notify anyone else in the area
  • Phone call 911
• Attempt to rescue the victim by breaking electrical contact with the energized source if it is safe to do so.
  
  • Exercise not endeavor to arroyo whatsoever areas where sparks or other visible electric activity is nowadays
  • First effort to turn off the source, preferably at a breaker or main. If these are not accessible, remove the plug or close off the supply
  • If there is no safe access to these points, attempt to move the victim with insulating material. Isolate yourself from the basis with plastic or wooden material, or even a phone directory. Endeavour to motility the victim with a long, insulating object such equally a wooden or fiberglass broomstick. Maintain maximum achievable distance betwixt yourself and the victim.
• Once the victim is safe and grounded check for response, including airway, animate and apportionment.
• If trained, perform CPR and apply an AED as needed.
• If no urgent status persists, care for the victim for burns and shock.^half-dozen
  
  • Lay the person down and elevate their anxiety above their head, unless head, cervix, spinal, broken hip or broken leg bones suspected.
  • Proceed the person warm, with a blanket if possible (fugitive serious burn down injuries)

Resources

Some all-time-practise data taken from interview with Ryan Norval, senior graduate pupil, and  Peter Weix, Head Engineer and Safety Officer at the Madison Symmetric Torus. The MST regularly utilizes high-voltages of 5 kV in standard operation and is used and maintained past over xx trained students, scientists, and operators.

Regulations

• University of Wisconsin Surround, Health & Condom: Burn down & Life Safe
• International Burn Lawmaking [pdf], Section 605, "Electrical Equipment, Wiring and Hazards"–Adopted past the City of Madison for public building standards.
• National Burn Protection Association: NFPA 70E- Electrical Safety
• Occupational Safety and Health Administration: OSHA 1910, Subpart S – Electrical; OSHA 1926.97, Electric Protective Equipment
• International Electrotechnical Committee

References

1. Gordon, Lloyd B., and Laura Cartelli. "A consummate electrical hazard classification system and its application." Electrical Safety Workshop, 2009. IEEE IAS. IEEE, 2009. [pdf]
2. United states of america Department Of Energy Electrical Condom Handbook (rev 2013) [pdf]
3. https://en.wikipedia.org/wiki/High_voltage
4. http://www.electricalsafetylab.com/resources.asp
5. Faircloth, D. C. "Technological aspects: high voltage." arXiv preprint arXiv:1404.0952 (2014).
6. British Carmine Cross Society, "Electrocution", https://www.redcrossfirstaidtraining.co.uk/News-and-legislation/latest-news/2011/March/Tip-of-the-month-Electrocution.aspx

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