PROTECTING YOUR STAFF FROM ARCING HAZARDS

Dr. David SweetingSweeting Consulting Pty Ltd

WHAT ARE ARCING HAZARDS?THREE PHASE TEST RIG

THREE PHASE AND SURROUND EARTH

WHAT DID YOU SEE

• Some people saw light• That is why it has been called an arc flash• Some saw Smoke? (Actually Copper Oxide

powder)• Most Heard Noise• Some may have seen copper droplets on floor• Many may have heard reports

– 1 person/day is burnt in USA

WHAT IS IT REALLY

• Free burning arcing fault• On parallel (not butted) electrodes• Totally dominated by magnetic forces• Producing a spray of 1083°C Copper droplets• Emitting light from the arc jets that can burn• Producing directed arc jets that can cut metal• Plus a plasma cloud that causes severe burns• Plasma can ignite clothing that burns victim

THREE PHASE AND SURROUND EARTH

PHYSICAL PICTURE

current arc jets plasma cloud

ARCING FAULT HAZARDS

• Severe burns from clothing igniting• Severe burns from plasma cloud• Burns/vision impairment from radiation (light)• Burns from molten copper droplets• Burns from burning aluminium droplets• Ventricular Fibrillation and arcs• Explosion and hearing issues

HIERARCHY OF HAZARDCONTROL MEASURES

• ANSI Z10 Table 1– 1.Elimination of the hazard– 2.Substitution of less hazardous equipment– 3.Engineering controls to reduce exposure or

severity– 4.Warnings signs and other communications– 5.Administrative controls, including practices– 6.Personal protective equipment

BRIEF HISTORY

• Arcing hazards have always existed• Concern about No. Electricians burnt in USA• In 1982 Ralf Lee published in IEEE Industry

applications and then campaigned• NFPA 70E introduced arc hazard assessment• In 2002 IEEE published 1584• OSHA mandated NFPA 70E in America• Then concern spread Interanationally

NFPA 70E and IEEE 1584• NFPA limited to prescribing PPE• NFPA 70E calculates parameters of arc• IEEE 1584 calculates parameters of arc• Both calculations based on the wrong physics

– Plasma not light causes 2nd degree burns– Maximum power transfer theorem does not apply– Plasma is a vector stream, not spherically uniform– Electrode direction is dominant

NFPA 70E and IEEE 1584

• Need understanding to “black box”• Perform the wrong tests

– Vertical electrodes to floor– Vertical electrodes into a box

• Misinterpret test result– Light is actually re-absorbed by copper vapour

• American Formulae out by factors of ten• Formulae in NENS9 Appendix A6.1

HAZARD ASSESMENT V

HAZARD EXPOSURE

• Electrician needs to perform a hazard assessment based on his hazard exposure.

• Can still perform a hazard exposure analysis and apply the first five risk control measures together with an appropriate PPE policy.

• For the sixth control measure the NENS9 Formulae are currently the most accurate.

WHAT CAN BE DONE• Consider live work• Design the system to fail safely• Design the system so that it is maintainable• Separate the person from the energy• Reward safe design features• Signage• Perform the correct protection studies• Ensure protection works• Adopt a suitable PPE policy

CONSIDER LIVE WORK

• Unavoidable live work– Operating, making safe, un-making safe– Testing, work in the vicinity

• Only work dead=No procedures• Only maintenance work can be done dead• Live work = written/approved procedures• Live work = training

CONSIDER LIVE WORK

• Work in the vicinity– Only one panel is dead– Incoming busbar is still alive– Not meant to be involved– Non Qualified/Approved workers– Visitors and Public

• Use designs made for live work– Computer rooms/ hospitals

DESIGN THE SYSTEM TO FAIL SAFELY

• The design system needs to include what happens when it fails.

• Use arc contained switchgear• Use fused leads with safety plugs on meters• Use Insulated tools

DESIGN THE SYSTEM SO THAT IT IS MAINTAINABLE

• Covers and bolts must be easy to replace so they are replaced.

• Require two bus-tie circuit breakers• Require a study to demonstrate everything

can be maintained• Provide safe thermal imaging

SEPERATE THE PERSON FROM THE ENERGY

• Install remote open/close panels• Use earthing trucks on medium voltage• Use separately fused control systems

SIGNAGE

• Ensure every cover that exposes hazardous conductors is labelled “XX volts behind”

• And never when it does not.• All signage = precise meaning• No over or under statement• Names must match• “Fed to” and “fed from” recommended

DO THE CORRECT PROTECTION STUDY

• 3 phase maximum case insufficient• Must do minimum fault levels

– Minimum utility, minimum transformers, – Include impedance to and along switchboard– Must take account of arc voltage at 400-440V

• Must do two-phase• Must do single phase• Should do others

ENSURE THE PROTECTION WORKS

• Will your protection see all faults?• Will your protection reset on triple current

zeros?

SUITABLE PPE POLICY

• Calculate the total energy in the arc at minimum fault levels.

• PPE must NOT support combustion• PPE must not melt on• PPE should be comfortable• Staff must want to use PPE• Normal PPE should cover droplets and light

CONCLUSIONS

• There is much that can be done to improve arc hazard safety for workers without relying solely on PPE and the incident energy from arc fault calculations that take no account of local conditions.