Tank Car Specialist Training Support Package November 2014 Module 11: Grounding and Bonding.

Tank Car Specialist

Tank Car SpecialistTraining Support Package

November 2014

Module 11: Grounding and Bonding

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Introduction

Static electricity is everywhere and it is likely present at the scene of any flammable liquids spill. Flammable and/or combustible liquids are major types of chemical spills we respond to as emergency responders. In order to effectively and safely mitigate an emergency involving flammable products, we need to know how to properly perform grounding and bonding.

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Objectives:11-1 The participant will be able describe what grounding and bonding is.

11-2 The participant will have the ability describe why we do grounding and bonding.

11-3 The participant will be able to describe the procedures for grounding and bonding.

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Definitions

• Electricity

• Volts

• Amperes

• Ohms

• Resistance

• Static Electricity

• Conductor

• Insulator

• Joules

• Grounding

• Bonding

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Capacitance• The ability of a material to

store or hold electrical energy

• Materials vary in their storage capacity

• Relaxation time is period it takes to equalize charges

• SIZE• MATERIAL

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Relaxation Time

• Time necessary for products to dissipate buildup of stored charges

• Times differ for various materials and products

• Consult chemical specific resources

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What Is Static Electricity?

• Caused by energy trapped on surface of non conductive molecules. – Can be created by the movement of

solids, liquids, and gases.

– Can be caused by contaminants such as:• Rust• Dirt• Dust

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Why Do Grounding and Bonding?

• What products:– Assess by Hazard

Class:

If it moves, it can produce a static charge.

Hazard

Class

Yes No

1

2

3

4

5

6

7

8

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Conditions for Ignition• There must be 4 conditions met

before static electricity discharge is a source:– There must be generation of static

electricity– There must be accumulation of charge – Discharge spark of sufficient energy– Discharge spark must be in flammable

atmosphere (LEL – UEL)

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Generation of Static Electricity• Problem occurs when there is:

– Accumulation – Discharge – static measured in joules

• .02 millijoules–Hydrogen, acetylene

• .25 millijoules–LPG (propane, C3H8)

• Must be in LEL – UEL– Propane – LEL 2.2 % – UEL 9.5 %

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Generation of Static Electricity

0

0.2

0.4

0.6

0.8

1

1.2

Millijoule Propane Acetylene,Hydrogen

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Controlling Static Electricity• Remove flammable atmosphere from area

– Vapor suppression

– Vapor dispersion

• Reduce production of static energy

– Slow the transfer down

• Release or “relax” the charge

– Ground and Bond – Best method

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Factors That Affect Grounding and Bonding

• Weather• Time of year• Temperature

0

10

20

30

40

50

60

JAN MAR MAY JULY SEPT NOV

Ohms

Cool, dry weather returns

Cold, dry weather

Spring thaw…warm, moist air

Very hot, Very dry

Monsoon

• Humidity• Moisture

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Seasonal Variation in Resistance

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Effect of Temperature on Resistance

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Factors That Affect Grounding and Bonding

• Soil type– Clay– Loam– Sand

• Moisture in soilHigher

moisture = lower

resistance

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Minimum Equipment Needed– Ground resistance meter– Intrinsically safe ohm meter– (4) ½” dia. or > copper grounding rods– (5) 50’ ¼” stainless steel braided cables with

appropriate connecting clips• 3 – Grounding cables (pinpoint and alligator clips)

• 2 – Bonding cables (pinpoint only)PinpointAlligator

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Additional Equipment for Grounding and Bonding

– Sledge hammer/post driver

– 4 foot long 4” x 4” post

– (10) ½” dia. or > copper grounding rods

– (10) ¼” stainless steel braided cables with alligator connecting clips• Length of cable is dependent on length of

rod

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The Wrong Way

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Before Grounding and Bonding

Don’t forget the basics:• Site safety• Vapor suppression (product dependent) - foam

• Detection and monitoring (product dependent)– LEL

• Operations level tactical– Damming, diking, retention, booms, pads, etc.

• Call Miss Utility, if conditions warrant

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Determining the Grounding Field• Will the soil/area absorb the charge?

– Assess the grounding field by:• Appropriate rod placement

–Maximum 50’ or length of cable <5’–Minimal traffic area

• Ground resistance meter–Different companies produce testing

devices–Operating principle is the same.

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Megger Unit

• Generates current and measures earth resistance through an internal OHM meter

• Unit is NOT intrinsically safe

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“Potential”

?

? ohms

?

Ground Field

Up Wind

Up Hill

Incident

75 ft.

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Acceptable Level for Resistance

• National Electrical Code (N.E.C.) establishes 25 ohms as ideal

• Petro Chemical of Canada sets 10 ohms

• Target is as low as practical

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Grounding FieldsHOUMA, LA PUEBLO, CO

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Safety Considerations

1 foot

2 feet

3 feet

4 feet

5 feet

NATURAL GAS

WATER

ELECTRICAL

SEWER

PHONE, CABLE TV

ALWAYS CHECK WITH ALL UTILITIES PROVIDERS BEFORE DRIVING RODS

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Resistance vs. Depth

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Rod Depth - Feet

Re

sist

ance

- O

hm

s

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Rod Spacing

28

4 ft

4 ft

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Adding WaterHOUMA, LA PUEBLO, CO

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Improving Ground Field• Add water to rods

• Add salt to water, copper sulfate orsodium carbonate

• Common rock salt most likely

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Adding Salt WaterHOUMA, LA PUEBLO, CO

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Location of the Fields

• Uphill and upwind

• Remote from immediate work area

• Ideally, set field 75-ft away

• Two fields offer redundancy

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Grounding and Bonding Sequence

1. Damaged/leaking container to ground

2. Receiving container to ground

3. Damaged/leaking container to receiving container

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GROUNDING FIELDS

GROUNDING CABLE

GROUNDING CABLE

BONDING CABLE

WIND

LEAKING VEHICLE

RECEIVING VEHICLE

Example of Grounding and Bonding Before Transfer

Pump

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Bad Connection PointsBolster not welded

to tank

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Bad Connection Points

Bolted, not WELDED to tank

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Bolted-on Handle

PackingGaskets / O - Rings

Bolted Flanges

Bad Connection Points

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Welded directly to tank

Good Connection Points

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TURNBUCKLE AREA

STEP / HANDRAILS

VALVES / FITTINGS

CENTER SILL

Mixed Connection Points

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NO TURNBUCKLEDirect weld to tank

Good Connection Points

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DIRECT WELD, BUT COVERED

IN PAINT, THERMAL

PROTECTION

DESIGNATED AREA

SCRAPED CLEAN

Good Connection Points

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Why Do Grounding and Bonding?• Applicable OSHA standard:

– 29 CFR 1910.106 – Flammable and Combustible Liquids (1910.106 (f) (3))

• NFPA– 30 Flammable and Combustible Liquids

Code.– 77 Recommended Practice on Static

Electricity

• NEC Article 250

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ConclusionParticipants have been given information to:

• Defined grounding and bonding and describe electricity, volts, amperes, ohms, static electricity, static transfer, static spark, conductor, insulator, breakdown voltage, capacitance, and joule. These basic terms are necessary to understand grounding and bonding

• Defined sources of static electricity, conditions of ignition, and ways to control static electricity hazards

• Listed factors that affect the ground field and describe how to check the ground field using an ohms earth tester

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ConclusionParticipants have been given the information to:

• Described where to locate the ground field and identify an acceptable level for resistance

• Established the recommended order for cable rod connection and container connection for grounding and bonding

• Given a situation in which grounding would be necessary, participants will be able to check the grounding field for correct resistance, demonstrate the proper sequence and position of the grounding connections, and proper location of the grounding field.

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