Arc Welding

Patrick V. BeboutBCN5737-8384 Advanced Construction Safety

Spring, 2009

Definition• Arc Welding – A fusion

process for joining metals. Through the application of intense heat, the metals at the joint intermix (often with a filler material) to create a metallurgical bond as strong as the original two metals.

Applications and Environment

• Arc welding is performed whenever an extremely strong metal bond is needed:– Construction– Maintenance– Manufacturing

• Arc welding is performed in all environments:– Indoors / Outdoors– Extreme Heights– Confined Spaces– Underwater

Arc Welding Components

• Arc Welding requires five main pieces of equipment:– Electrode – Electrode Holder – Electrode Cable– Welding Machine (AC or

DC)– Work Cable

Arc Welding Components

• The Welding machine– Supplies the electricity

needed to create the welding arc

– Converts 120-240 volt AC electricity to welding voltage, typically 20-30 volts AC (also DC voltages)

Lincoln Electric’s AC-225 with Wheel Kit and Gloves

The Arc Welding Process

• How it works:– The intense heat needed to

melt metals is created by the electric arc (> 6500 °F)

– The arc forms between the electrode and the work surface

– The welder guides the arc along the joint by moving the electrode

History of Arc Welding

• The electric arc was discovered by Sir Humphry Davy in 1808

• N.G. Slavianoff and C.L. Coffin developed metal electrodes in the late 1800’s

• Around 1900, A.P. Strohmenger stabilized the arc with coated metal electrodes

• In 1919, C.J. Holslag invented AC welding

Portrait by Henry Howard, 1803

Sir Humphry Davy

History of Arc Welding

• By WWI, welding began replacing rivets on ships due to time savings

• By the end of the war, Germans, Americans and British were arc welding ships and airplanes

• Other advances to strengthen the welds led to much larger usage by WWII

Source: www.wikipedia.org

Dangers of Welding

• Most fatalities that occur while welding fall into four categories*:– Falls– Crushed / Struck-By– Fire / Explosions– Electrocution

“Welding, cutting and brazing are hazardous activities ... The risk from fatal injuries alone is

more than four deaths per 1,000 workers over a working lifetime.”

- OSHA Safety and Health Topicshttp://www.osha.gov/SLTC/weldingcuttingbrazing/index.html

* Information extracted from OSHA construction worker fatality data (1990-2007)

Types of Welding Fatalities

0

10

20

30

40

50

60

Falling

Crushed /Struck-By

Fire /Explosion

Electrocution

Other

Percentageof Fatalities

Source: Information extracted from OSHA construction worker fatality data (1990-2007)

Example Fatality

• Fall:– Employee #1 was walking along

the edge of a roof to conduct some welding on an airport expansion project

– Decking along the edge became loose

– The employee fell 51 feet to the compacted soil

– He died several hours later of internal bleeding and asphyxia

Source: OSHA construction worker fatality data (1990-2007)

Example Fatality

• Crushing Injury:– Employee #1 was welding pre-cast

panels into place at a water treatment facility

– After welding the first panel, Employee #1 repositioned to complete a corner weld on the second panel

– The first panel fell over and crushed him from the rib cage down

– Employee #1 died

Source: OSHA construction worker fatality data (1990-2007)

Example Fatality

• Explosion:– 3 Workers were making repairs on a

crude oil storage tank with an arc welder

– 90 gallons of oil had been placed in the tank the previous day

– Vapors from the tank were ignited by the welding arc

– Workers #1 and #2 were killed instantly in the explosion

– Worker #3 died the next day from burns covering 90% of his body

Source: OSHA construction worker fatality data (1990-2007)

Example Fatality

• Electrocution:– Employee #1 was arc welding on his

back, drenched in his own sweat– His equipment was set at 135

ampere AC position– Equipment was in excellent

condition, with warning labels concerning amperage

– Employee was later found dead– Medical Examiner confirmed that he

died from electrocution

Source: OSHA construction worker fatality data (1990-2007)

Other Dangers

• Eye damage from flash burns or Ultraviolet (UV) Radiation (“Welder’s Eye”)

• Flash burns to the welder or surrounding workers

• Inhalation of dangerous fumes (“Metal Fume Fever”)

• Heat stress

OSHA & Arc Welding

• OSHA addresses arc welding with Regulations 1926.351

• Manual Electrode Holders:– Only use electrode holders specifically designed to

safely handle the maximum rated current required– Make sure all current carrying parts are well

insulated

OSHA & Arc Welding

• Welding Cables and Connectors:– All welding cables should be well insulated

– Repairs or splices must be at least 10ft from the electrode. Splices made closer must have the same insulating quality as the cable.

10’ Min.

Repair or splice

OSHA & Arc Welding

– Use substantial insulating material at splices or connectors

– Cables in need of repair can not be used

Splice

OSHA & Arc Welding

• Ground Returns and Machine Grounding:– Ground cables must be able to carry the specified

maximum current capacity

– Do not use pipes carrying flammable gases, flammable liquids, or electric wires as a ground

Ground Wire

Flammable Gases / Liquids

Electrical Wiring

OSHA & Arc Welding

– Must maintain electrical contact at all joints– Joints to be bonded and periodically inspected for

electrolysis or fire hazard (when continuously employed as ground return)

Joints

OSHA & Arc Welding

– Frame of welding machine must also be grounded– Ground must be able to break fuse

– Ground connections must be strong and adequate

Must Also be Grounded

OSHA & Arc Welding

• Operating Procedures:– When left unattended, remove electrodes and

place away from conductive materials – Never place hot electrode holders in water

Hot Electrode Holder

OSHA & Arc Welding

– Turn off welding machine when left unattended or when moving

– Use shielding screens if possible

Additional Safety Guidelines

• Avoid crushing injuries and falls:– Examine the workspace

prior to commencing any work to identify possible hazards

– Always properly tie-off when welding from heights

– Wear a life-jacket when working above water

FALL HAZARD

Additional Safety Guidelines

• Minimize Risk of Electrocution:– Low-level dampness increases the risk of electrocution.

Do not weld in a wet or damp environment unless an insulating mat or other non-conductive material is securely in place between all body contact points and any surrounding metal.

– Minimize electrical shock through proper equipment:• Dry gloves, rubber-soled shoes & dry clothing• Frequent changing of cotton liners to prevent welding

gloves saturated with perspiration• Standing or sitting on a dry wooden floor, a dry rubber

mat or similar insulating material

Additional Safety Guidelines

• Avoid the risk of explosion:– Where possible welding should be undertaken

outdoors in a well ventilated area– Open up structures / containers prior to welding– Ventilation during cleaning should be such that

any flammable gases are quickly and safely dispersed

– Sight or smell must not be used to determine if safe working conditions apply

– If the condition of the container is not known, it should be assumed that the container contains an explosive mixture

Personal Protective Equipment

Source: National AG Safety Databasehttp://www.cdc.gov/nasd/docs/d000801-d000900/d000873/d000873.html

• Wear the appropriate PPE for the job:– Eye Protection– Burn Protection– Inhalation Protection

Conclusions

• Welding should only be carried out by experienced welders directly supervised by a person who fully understands the hazards involved

• Always properly maintain equipment• Wear appropriate personal protective

equipment• Perform a hazard identification and

risk assessment of any workplace prior to commencement of any work