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Electrostatic Evaluation of the Propellant Handlers Ensemble

Electrostatics and Surface Physics LaboratoryNASA

Kennedy Space Center, FL

Michael D. Hogue, PhDCarlos I. Calle, PhD

Charles R. Buhler, PhDMindy Ritz

Jeff Starnes

Mail stop: KT-EKennedy Space Center, FL 32899

(321) 867-7549Michael.D.Hogue@nasa.gov

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AgendaBackgroundBackgroundElectrostatic TestingElectrostatic Testing

Surface & Volume ResistivitySurface & Volume ResistivityCorona ChargingCorona ChargingTriboelectric ChargingTriboelectric ChargingSpark IncendivitySpark Incendivity

SummarySummary

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BackgroundThe Kennedy Space Center (KSC) uses SelfThe Kennedy Space Center (KSC) uses Self--Contained Atmosphere Protective Ensemble Contained Atmosphere Protective Ensemble (SCAPE) suits to protect technicians during (SCAPE) suits to protect technicians during hazardous fuel and oxidizer loading operations.hazardous fuel and oxidizer loading operations.Among the fuels are Hydrazine, monomethyl Among the fuels are Hydrazine, monomethyl hydrazine (MMH), and unsymmetrical dimethyl hydrazine (MMH), and unsymmetrical dimethyl hydrazine (UDMH) which are all very toxic as hydrazine (UDMH) which are all very toxic as well as flammable.well as flammable.The SCAPE suit fabrics tested are: Chloroprene, The SCAPE suit fabrics tested are: Chloroprene, VFH Copolymer, ChlorobutylVFH Copolymer, Chlorobutyl--coated Nomex, coated Nomex, Bromobutyl, and PTFEBromobutyl, and PTFE--coated fabric.coated fabric.Also the boot and glove of the current PHE were Also the boot and glove of the current PHE were tested for surface resistivity.tested for surface resistivity.

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Background

KSC has performed a variety of electrostatic KSC has performed a variety of electrostatic evaluations on candidate Selfevaluations on candidate Self--Contained Contained Atmosphere Protective Ensemble (SCAPE) Atmosphere Protective Ensemble (SCAPE) fabrics as well as the current Propellant fabrics as well as the current Propellant Handlers Ensemble (PHE) fabric used at KSC Handlers Ensemble (PHE) fabric used at KSC for propellant operations [1].for propellant operations [1].These tests are surface resistivity, volume These tests are surface resistivity, volume resistivity, corona charging, triboelectric resistivity, corona charging, triboelectric charging, and spark incendivity.charging, and spark incendivity.

[1] C. R. Buhler, C. I. Calle, “Electrostatic Evaluation SCAPE Suit Materials”, ESPL-TR05-005, July 21, 2005.

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Electrostatic Testing – Surface & Volume Resistivity

Surface resistance is the ratio of the DC voltage Surface resistance is the ratio of the DC voltage to the current flowing between two electrodes of to the current flowing between two electrodes of specified configuration that contact the same specified configuration that contact the same side of the material and is expressed in ohms side of the material and is expressed in ohms ((ΩΩ).).Surface resistivity measurements performed at Surface resistivity measurements performed at KSC meet the requirements of the ESD KSC meet the requirements of the ESD Association Standard Test Method ESD Association Standard Test Method ESD STM11.11, STM11.11, ““Surface Resistance Measurements Surface Resistance Measurements of Static Dissipative Planar Materialsof Static Dissipative Planar Materials””, (2001)., (2001).

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Electrostatic Testing – Surface & Volume Resistivity

Volume resistance is the resistance measured in Volume resistance is the resistance measured in ohms through the bulk of the material and is ohms through the bulk of the material and is expressed in ohmexpressed in ohm--cm (cm (ΩΩ--cm).cm).Volume resistivity measurements performed at Volume resistivity measurements performed at KSC meet the requirements of the ESD KSC meet the requirements of the ESD Association Standard Test Method ESD Association Standard Test Method ESD STM11.12, STM11.12, ““Volume Resistivity Measurements Volume Resistivity Measurements of Static Dissipative Planar Materialsof Static Dissipative Planar Materials””, (2001)., (2001).

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Surface & Volume Resistivity Test Equipment

PRS-801 Resistance measurement system

Concentric ring electrode per ESD test standards STM11.11 and 11.12

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Surface & Volume Resistivity Tests –Example Data

Surface and volume resistivity tests for Chlorobutyl-coated Nomex Fabric

Material is highly insulative in both tests.

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Surface Resistivity of PHE Boot & Glove

1

2

3

4

5

6

1

2

3

All locations on the boot are static dissipative (GΩ) except for the top band at location 6 which is insulative (TΩ).

All locations on the glove are conductive (KΩ) except for location 3 which is insulative (TΩ).

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Electrostatic Testing – Corona Charging

Corona charging is when air molecules are Corona charging is when air molecules are ionized by a strong electric field, usually ionized by a strong electric field, usually created at sharp needle electrodes created at sharp needle electrodes energized at a high voltage, and placed energized at a high voltage, and placed near a target surface.near a target surface.The corona charging device used at KSC The corona charging device used at KSC conforms to British Standard BS 7506, conforms to British Standard BS 7506, ““Methods for Measurements in Methods for Measurements in Electrostatics, Part 2Electrostatics, Part 2””, (1995)., (1995).

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Corona Charging Test Equipment

JCI 155v5 (John Chubb Instruments)

±10,000 volts

Charge decay measurements (voltage decays to 1/e or 37% of maximum in one second or less)

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Corona Charging Tests – Example Data

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Corona Charging Tests – Application of Staticide™ Anti-static Compound

To improve the charge decay of current PHE To improve the charge decay of current PHE used at KSC, a commercial antiused at KSC, a commercial anti--static compound static compound called Staticidecalled Staticide™™ is applied to the surface of the is applied to the surface of the suit. suit. However, StaticideHowever, Staticide™™ is difficult to apply evenly is difficult to apply evenly and wears off quickly in field conditions at KSC.and wears off quickly in field conditions at KSC.A series of corona charging tests using mixtures A series of corona charging tests using mixtures of of StaticideStaticide™™ with a commercial liquid detergent with a commercial liquid detergent and Isopropyl alcohol (IPA) were performed to and Isopropyl alcohol (IPA) were performed to determine if these formulations improve the determine if these formulations improve the coverage and longevity of coverage and longevity of StaticideStaticide™™..

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Corona Charging with Staticide™ MixturesThe use of full StaticideThe use of full Staticide™™ (no additive used, applied (no additive used, applied same day as use) is sufficient to bring the charge decay same day as use) is sufficient to bring the charge decay properties into acceptable limits (decay time to 1/e is properties into acceptable limits (decay time to 1/e is under 1 sec). under 1 sec).

If the suit is to be used the next day after application of If the suit is to be used the next day after application of the Staticidethe Staticide™™, use a mixture of 5 parts liquid detergent , use a mixture of 5 parts liquid detergent to every 100 parts Staticide. This mixture has to every 100 parts Staticide. This mixture has significantly better charge decay properties than full significantly better charge decay properties than full StaticideStaticide™™ applied 24 hours ahead of time.applied 24 hours ahead of time.

The use of IPA as an additive to StaticideThe use of IPA as an additive to Staticide™™ has no has no significant positive affect on the properties of Staticidesignificant positive affect on the properties of Staticide™™, , because of this it should not be used for this application.because of this it should not be used for this application.

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Electrostatic Testing – Triboelectric Charging

Triboelectric charging is caused by contact or Triboelectric charging is caused by contact or rubbing of two materials together.rubbing of two materials together.KSC uses Standard Test Method MMAKSC uses Standard Test Method MMA--19851985--79 79 for triboelectric tests.for triboelectric tests.This method records the charge decay after the This method records the charge decay after the test material is rubbed with either a wool or test material is rubbed with either a wool or PTFE felt wheel.PTFE felt wheel.The KSC standard requires that the resulting The KSC standard requires that the resulting voltage on a material decay below 350 volts in voltage on a material decay below 350 volts in 5.0 seconds after separation from the rubbing 5.0 seconds after separation from the rubbing wheel.wheel.

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Triboelectric Test Apparatus

Test Conditions per MMA-1985-79:

30% & 45% relative humidity.

400 rpm.

5.0 lbs of force.

10 second rubbing period to saturate sample with charge.

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Triboelectric Testing – Example Data

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Spark Incendivity TestingSpark Incendivity TestingSpark Incendivity Testing is commonly used throughout the industry to evaluate the electrostatic hazard for packaging/handling materials such as Flexible Intermediate Bulk Containers (FIBC’s).

The test is performed in accordance with Test Standard IEC:2003 61340-4-4, “Electrostatic classification of Flexible Intermediate Bulk Containers (FIBCs)”.

Spark Incendivity Probe

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The incendivity Probe was used with hydrogen gas which The incendivity Probe was used with hydrogen gas which has a Minimum Ignition Energy (MIE) of 0.02 has a Minimum Ignition Energy (MIE) of 0.02 mJmJ..Ambient RH (50Ambient RH (50--60%) and low RH (2060%) and low RH (20--25%)25%)Samples mounted vertically in an Insulating Frame Samples mounted vertically in an Insulating Frame

Spark Incendivity Testing Using Gas ProbeSpark Incendivity Testing Using Gas Probe

Clean Room Test Chamber

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Spark Incendivity Testing Using Gas Spark Incendivity Testing Using Gas ProbeProbe

Charging MethodsCharging MethodsCorona Charging Corona Charging –– using a using a corona/static brush and a corona/static brush and a highhigh--voltage power supply voltage power supply (negative polarity at 30kV DC).(negative polarity at 30kV DC).TriboTribo--Charging Charging –– using a 5using a 5””diameter rotating diameter rotating ““woolwool--coveredcovered”” disc or PTFE disc.disc or PTFE disc.

Surface Potential Surface Potential MeasurementsMeasurements

Used a JCI 140 to characterize Used a JCI 140 to characterize the surface potential applied the surface potential applied to the surface after deposition to the surface after deposition of of tribotribo charge or corona charge or corona charge.charge.

Tribo Charger

Corona Charger

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Minimum Ignition Energies of Hypergolic Fuels used at KSC (In Air)

9.6 mJ9.6 mJ4.4 mJ4.4 mJ5% Hydrazine 5% Hydrazine 1 mm spacing **1 mm spacing **

Ignition EnergyIgnition Energy100% Ignitions100% Ignitions

Ignition EnergyIgnition Energy16% Ignitions16% Ignitions

3.2 mJ3.2 mJ2.7 mJ2.7 mJ4.3% UDMH @ 300 4.3% UDMH @ 300 ΩΩmm(unsymmetrical (unsymmetrical dimethylhydrazine)*dimethylhydrazine)*

3.4 mJ3.4 mJ2.8 mJ2.8 mJ2.2% MMH @ 300 2.2% MMH @ 300 ΩΩm m (monomethylhydrazine)*(monomethylhydrazine)*

Ignition EnergyIgnition Energy100% Ignitions100% Ignitions

Ignition EnergyIgnition Energy33% Ignitions33% Ignitions

* Hornung, Davis and Baker, “Determination of the Minimum Ignition Energy for Monomethylhydrazine (MMH) and Unsymmetrical Dimethylhydrazine (UDMH)”, WSTF-IR-98-0105 (1998).

** Hornung, Haas, and Baker, “Determination of Nitrogen and Helium Diluent Effects on the Ignition Energy of Hydrazine”, WSTF-IR-0949-001-02 (2002).

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Discharge Incendivity Testing Using Gas ProbeDischarge Incendivity Testing Using Gas Probe

Spark Incendivity Probe – Approach the charged sample several times to check for an ignition of the gas mixture of known MIE. (Approach at 0.5-1.0 m/s)Repeat Procedure – Repeat these steps at least 25 times per side.

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Discharge Incendivity Testing ResultsDischarge Incendivity Testing Results

No Ignitions were detected in any of the No Ignitions were detected in any of the SCAPE suit fabrics.SCAPE suit fabrics.Ignitions were detected with the ChlorobutylIgnitions were detected with the Chlorobutyl--coated Nomex fabric in the presence of a coated Nomex fabric in the presence of a metal backing. The metal backing metal backing. The metal backing concentrated the electric field lines on the concentrated the electric field lines on the fabric surface.fabric surface.The fabrics by themselves, without the The fabrics by themselves, without the presence of a metal surface in the interior of presence of a metal surface in the interior of the suit, should not produce any sparks with the suit, should not produce any sparks with enough energy to ignite hypergolic fuels.enough energy to ignite hypergolic fuels.

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Summary

All SCAPE fabrics tested for surface and All SCAPE fabrics tested for surface and volume resistivity are highly insulative.volume resistivity are highly insulative.Most of the SCAPE suit fabrics tested to Most of the SCAPE suit fabrics tested to corona charge decay failed to discharge to corona charge decay failed to discharge to 37% or 1/e of their initial voltage in less 37% or 1/e of their initial voltage in less that one second.that one second.Both sides of the Chloroprene fabric Both sides of the Chloroprene fabric passed the corona discharge requirement passed the corona discharge requirement at both room and low humidity.at both room and low humidity.

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Summary

Most of the SCAPE suit fabrics tested for Most of the SCAPE suit fabrics tested for triboelectric charge decay failed to discharge triboelectric charge decay failed to discharge below 350 volts in five seconds.below 350 volts in five seconds.All the SCAPE suit fabrics passed the spark All the SCAPE suit fabrics passed the spark incendivity tests except for a few cases where incendivity tests except for a few cases where metal backing was applied to the fabric.metal backing was applied to the fabric.Despite being highly insulative and many failing Despite being highly insulative and many failing the corona and triboelectric tests, the SCAPE the corona and triboelectric tests, the SCAPE fabrics passed the spark incendivity tests and fabrics passed the spark incendivity tests and are safe to use under their operating conditions are safe to use under their operating conditions at KSC.at KSC.