Correlating Welding Arc Time and Correlating Welding Arc Time and Field Derived Generation RatesField Derived Generation Rates

-- PO132 PO132 --American Industrial Hygiene Association’s

67th Annual Conference and ExpositionJune 7, 2007, Philadelphia, Pennsylvania

F.W. Boelter, CIH, PEC.E. Simmons, CIH

G.A. Vos, PhD

Boelter Associates, Inc.Park Ridge, IL

Problem Statement

Would it be feasible to develop a reliable model utilizing anecdotal information related to welding arc time, coupled with laboratory sourced fume generation data to reliably predict concentrations in the breathing zone?To answer this, we performed this investigation, with the goal of answering 2 primary questions:

How reliable are subjective estimates of arc time?How does arc time relate to breathing zone concentrations?

Potential VariablesPotential VariablesWelding processWelding processWelding consumableWelding consumable

Consumable diameterConsumable diameterConsumable composition (usually alloy matched)Consumable composition (usually alloy matched)

Base metal Base metal -- i.e. stainless steel, mild steel, etc.i.e. stainless steel, mild steel, etc.Presence of coatings or paints on the base metalPresence of coatings or paints on the base metalWhether performed indoors or outdoorsWhether performed indoors or outdoorsConfiguration of the spaceConfiguration of the spaceElectrical current and voltageElectrical current and voltageAmount and type of ventilationAmount and type of ventilationWelderWelder’’s skill and speeds skill and speedPosition of the welderPosition of the welderPersonal protective equipmentPersonal protective equipmentFume/Gas quantity, dependent upon several parameters:

AlloyAmperageVoltageShieldingPolarity

WelderWelder’’s arc time or % time weldings arc time or % time welding

Complicating the Measurement of Welding Complicating the Measurement of Welding ––Many Related Terms with Differing DefinitionsMany Related Terms with Differing Definitions

Arc timeArc timeWelding timeWelding timeLength of time arc is maintainedLength of time arc is maintainedNonNon--arc time/handling timearc time/handling timeDuty cycleDuty cycleOperating factorOperating factorOperator factorOperator factorHours per shiftHours per shiftDeposited metal/deposition rateDeposited metal/deposition rate

AWS Welding HBAWS Welding HB–– 99thth Ed, V1Ed, V1

Chung 1999 Chung 1999 -- pg 111pg 111

CastnerCastner 1998 1998 –– pg 228spg 228s

NIOSH 1979 NIOSH 1979 –– pg 14pg 14

How reliable are subjective estimates of arc time?

InterInter--Rater ReliabilityRater ReliabilityReliability of subjective measures could have an impact on any Reliability of subjective measures could have an impact on any modeling based upon such datamodeling based upon such dataTherefore interTherefore inter--rater reliability of subjective IH welding rater reliability of subjective IH welding judgments was assessed judgments was assessed 19 video clips of single welding cycles were shown to 9 19 video clips of single welding cycles were shown to 9 experienced hygienists experienced hygienists (including 3 clips shown in this presentation)(including 3 clips shown in this presentation)

Raters were asked to provide judgments for 8 variables per clip:Raters were asked to provide judgments for 8 variables per clip:Determination of if welding was being performed Determination of if welding was being performed (Y/N)(Y/N)

Subjective estimate of daily time spent welding in a given job Subjective estimate of daily time spent welding in a given job (Hrs.)(Hrs.)

Estimates of the arc time for a job, as both:Estimates of the arc time for a job, as both:Percent of an 8 hour shift Percent of an 8 hour shift (%)(%)

Time in minutes Time in minutes (Min)(Min)

The type of welding being performed The type of welding being performed (e.g. MIG, TIG, SMAW, etc.)(e.g. MIG, TIG, SMAW, etc.)The type of metal being welded The type of metal being welded (e.g. Steel, Aluminum, etc.)(e.g. Steel, Aluminum, etc.)Whether or not the welder was wearing a welding hood Whether or not the welder was wearing a welding hood (Y/N)(Y/N)

And if so, the type of hood being used And if so, the type of hood being used (e.g. PAPR)(e.g. PAPR)

Tee ShirtTee Shirt

Red ShirtRed Shirt

Green ShirtGreen Shirt

InterInter--Rater ReliabilityRater Reliability

Reliability measures for all subjective estimates of time relateReliability measures for all subjective estimates of time related variables were fairly low.d variables were fairly low.This could negatively impact modeling and other related assessmThis could negatively impact modeling and other related assessments when subjective time ents when subjective time estimates are used in lieu of actual quantitative measures.estimates are used in lieu of actual quantitative measures.Thus when data is used for modeling and other advanced calculatiThus when data is used for modeling and other advanced calculations, actual quantitative ons, actual quantitative measurements of time related variables should be used rather thameasurements of time related variables should be used rather than subjective estimates. n subjective estimates.

“Excellent” reliability for:- Judgments of welding- Whether a hood was worn

“Fair to Good” reliability for:- Welding type- Metal involved- Hood type

“Poor to Fair” reliability for:- Time spent welding in hours- Arc time (both % of shift and minutes)

Variable Data Type Raters Cases Statistic Value 95% CI pWelding Dichotomous 9 19 KR‐20 0.97

9 19 Percent Agreement 93% (71%, 100%)Time Welding (Hrs)* Continuous 6* 19 ICC(2,1) Absolute Agreement, Single Measures 0.31 (0.10, 0.56) < 0.001Arc Time (%)* Continuous 6* 19 ICC(2,1) Absolute Agreement, Single Measures 0.56 (0.37, 0.76) < 0.001Arc Time (Min)* Continuous 5* 19 ICC(2,1) Absolute Agreement, Single Measures 0.46 (0.24, 0.69) < 0.001Welding Type Nominal 9 19 Percent Agreement 73% (47%, 100%)Metal Involved Nominal 9 19 Percent Agreement 73% (38%,100%)Welding Hood* Dichotomous 8* 19 KR‐20 0.96

9 19 Percent Agreement 88% (66%, 100%)Welding Hood Type Nominal 9 19 Percent Agreement 73% (23%, 100%)* When raters judged any given job as "not welding," other variables were somtimes left blank, resulting in an unbalanced dataset.

    Thus some statistcs where calculated using all cases but excluding the missing raters

How does arc time relate to breathing zone concentrations?

Breathing Zone ConcentrationsBreathing Zone Concentrations

Breathing zone concentrations of welding performed by a pipe Breathing zone concentrations of welding performed by a pipe fitter doing his normal real world welding tasks in the field wefitter doing his normal real world welding tasks in the field were re evaluatedevaluatedWelding type was SMAW, performed indoorsWelding type was SMAW, performed indoorsMultiple 15 minute samples were collected during actual arc Multiple 15 minute samples were collected during actual arc welding tasks, both inside the welding hood and outside the welding tasks, both inside the welding hood and outside the hoodhood

Samples and Percent Arc TimeSamples and Percent Arc Time

Correlation of Arc Time and Concentrations –In Hood Samples

Sample Percent Arc Time Total Particulate (mg/m^3)

Fe (mg/m^3)

Mn (mg/m^3)

1 20% 4 0.42 0.042 37% 3.37 0.59 0.123 30% 3.43 0.6 0.144 30% 4.47 0.8 0.185 23% 3.4 0.48 0.11r -0.22 0.61 0.62p (sig.) 0.72 0.28 0.26r² 0.05 0.37 0.39

Correlation of Arc Time and Concentrations –Out of Hood Samples

Sample Percent Arc Time Total Particulate (mg/m^3)

Fe (mg/m^3)

Mn (mg/m^3)

1 20% 4.47 0.95 0.112 37% 3.47 0.51 0.113 30% 0.36 0.074 30% 5.2 0.72 0.165 23% 0.37 0.08r -0.49 -0.40 0.18p (sig.) 0.67 0.50 0.77r² 0.24 0.16 0.03

ConclusionsConclusionsHow reliable are subjective estimates of arc time?

InterInter--rater reliability measures for subjective estimates of time relarater reliability measures for subjective estimates of time related variables were low, which ted variables were low, which could have a negative impact on models using such estimatescould have a negative impact on models using such estimatesThus when arc time data is used for modeling and other advanced Thus when arc time data is used for modeling and other advanced calculations, actual quantitative calculations, actual quantitative measurements of time related variables would be critical.measurements of time related variables would be critical.

How does arc time relate to breathing zone concentrations?No significant or strong No significant or strong correlationscorrelations for arc time and breathing zone concentrations for arc time and breathing zone concentrations werewere found found Arc time on its own appears to be a poor predictor of exposureArc time on its own appears to be a poor predictor of exposure

Can we develop a model that utilizes anecdotal information related to welding arc time, coupled with laboratory sourced fume generation data to reliably predict concentrations in the breathing zone?

Not according to these findingsNot according to these findingsThese results emphasize the need for fieldThese results emphasize the need for field--derived welding concentrations and emission rates for derived welding concentrations and emission rates for estimation of exposures estimation of exposures Models based primarily upon arc time and laboratory fume generatModels based primarily upon arc time and laboratory fume generation rates using self reported ion rates using self reported estimates of welding time would likely yield estimates of exposuestimates of welding time would likely yield estimates of exposure grossly in errorre grossly in error

Recommendations for future study:Recommendations for future study:Determination of what variables do highly correlate with welding fume exposures, so that reliable and reproducible models can be developedLab based fume generation rates are often developed with protocols and parameters that do not reflect real world welding practices, thus additional research is needed to derive more applicable values so that they may be included in the development of future models

LiteratureLiterature

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Adjectives that can be used in ICC Assessment:Adjectives that can be used in ICC Assessment:Fleiss, J.L.: The Design and Analysis of Clinical Experiments. NFleiss, J.L.: The Design and Analysis of Clinical Experiments. New York: John ew York: John Wiley & Sons, Inc., 1986.Wiley & Sons, Inc., 1986.

Correlating Welding Arc Time Correlating Welding Arc Time and Field Derived Generation and Field Derived Generation

RatesRates

Fred W. Boelter, CIH, PEFred W. Boelter, CIH, PEBoelter & Yates, Inc.Boelter & Yates, Inc.Park Ridge, IllinoisPark Ridge, Illinois

847/692847/692--47004700fboelter@boelterfboelter@boelter--yates.comyates.com