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A risk assessment takes into account both the hazards and the likelihood that those hazards would occur

to determine risk. There are a number of general risk assessment procedures available and it is

recommended to use a procedure already in place, if one exists. Some risk assessment procedures are:

EN ISO 14121, Principles for risk assessment, and the associated technical report (ISO/TR-14121-2).EN ISO 10218-1, Industrial Robots.

ISO 12100, Safety of machinery General principles for design Risk assessment and risk reduction

IEC/EN 61508, Functional safety of electrical, electronic and programmable electronic safety-relatedsystems.

IEC/EN 61511,Functional safety - Safety instrumented systems for the process industry sector

ANSI B11.TR3 , Risk assessment and risk reduction A guide to estimate, evaluate and reduce risksassociated with machine tools

ANSI RIA R15.06 , Safety Requirements for Industrial Robots and Robot Systems

ANSI PMMI B155.1, Safety Requirements for Packaging Machinery and Packaging RelatedConverting Machinery

ASSE Z224.1, Control of Hazardous Energy, Lockout/Tag out and Alternative Methods

All risk assessment methodologies require identification of specific tasks, identification of the hazards,quantifying the severity of the hazard without safeguards, and quantifying the likelihood of the hazard

with safeguards in place. Some risk assessment methodologies also include quantification of a

likelihood of avoidance or escape from injury. As electrical hazards occur at a rate far greater thanhuman reaction times (milliseconds), it is recommended that the likelihood of avoidance be considered

extremely unlikely should the hazard occur.

In terms of electrical hazards, one of the hazard assessment procedures described in Annex D is

recommended for arc flash. It is recommended that the shock hazard be assessed using one of the

following methods:

-IEEE Standard 80 or Standard 516 which quantifies whether a shock hazard would be considered fatal.-Consider all shock hazards under 50 volts as nonfatal and those over 50 volts as fatal, as described in

Article 130.

When considering the likelihood of a hazard, it is recommended to use an absolute approach to shock

hazards as described in IEEE Standard 516-2009, IEEE Standard C2 (NESC), OSHA 1910.269, and

OSHA 1910.333. That is, shock likelihood is conservatively estimated at 100% at a given distance froman exposed conductor.

When considering the likelihood of an arc flash hazard, particular attention must be paid to the taskanalysis itself. If the likelihood of occurrence is driven by human reliability, such as using a conductive

tool such as a screwdriver in the vicinity of exposed conductors to make an adjustment, then given the

much greater likelihood of human errors, equipment reliability can be safely ignored and only the

human performance addressed.

Informational note: Support for this conclusion is given in Workplace Electrical Injury and Fatality

Statistics, 2003-2010, ESFI (2012), which shows that according to U.S. Bureau of Labor Statistics,burn injuries related to electrical equipment occur at a rate of approximately 0.1 incidents per 10,000

workers per year, far greater than reported equipment failure rates. Further, Arc flash hazard analysis

and mitigation, Inshaw and Wilson, Protective Relay Engineers 2005 58th Annual Conference,indicated that human error was the cause in 80% of injuries related to electrical equipment based on

U.S. Bureau of Labor Statistics.

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Generally human error rates have been determined to be between 1% and 40% with an average value of

approximately 10%. Recommended guidance for detailed methods to quantifying human reliability is

given in:

-IEEE Standard 1082 (1997): IEEE Guide for Incorporating Human Action Reliability Analysis forNuclear Power Generating Stations

-Kirwan, B. (1994) A Guide to Practical Human Reliability Assessment. CPC Press.

-Kirwan, B. (1996) The validation of three human reliability quantification techniques - THERP,HEART, JHEDI: Part I -- technique descriptions and validation issues. Applied Ergonomics. 27(6) 359-

373.

-SHEAN (Simplified Human Error Analysis code) and automated THERP, J.R. Wilson, WestinghouseIdaho Nuclear Company

Finally when considering safe guards for arc flash, IEEE 1584-2001 states that if PPE meeting therequirements described in the referenced ASTM standards are worn, the likelihood of a life altering or

fatal injury is reduced by 90%. This figure is primarily driven by the inherent difficulty in quantifying

the long tail distribution of the incident energy values. Thus it should be considered that even if

wearing PPE meeting or exceeding the calculated incident energy given any calculation method, thereis still a small residual risk of an arc flash injury which may lead to a conclusion that the task must be

redesigned and that reliance on PPE alone for arc flash hazards is insufficient.

If likelihood of a hazard is driven primarily by equipment failure rates, one condition must be met.

Equipment reliability data is reported only for good or average maintenance. Improper

maintenance or installation would necessarily lead to much higher failure rates. Article 200 givesguidance on proper maintenance and installation requirements. Failure rates for arcing faults are

generally well below 10-5. Reliability data for electrical equipment given this information is given in

the following references:

-IEEE 493-2009: Recommended Practice for the Design of Reliable Industrial and Commercial PowerSystems. Note: Tables provide both failure rates and failure modes (arcing, all as well as line-to-

ground)

-Offshore Reliability Data Handbook 5th Edition, Volume 1 Topside Equipment, Volume 2 SubseaEquipment (OREDA 2009).

-IEEE 500-1984, IEEE Guide to the Collection and Presentation of Electrical, Electronic, Sensing

Component, and Mechanical Equipment Reliability Data for Nuclear-Power Generating Stations Note:Out of print.

-Willis, Electric Power Distribution Reliability 2nd Edition. Note: Utility-specific data and does not

provide arcing fault-specific data.