Jerzy Jurewicz & Boulos_Analysis of safety aspects associated with the plasma synthesis and handling...

Analysis of safety aspects associated with the plasma synthesis and handling of nanopowders – from design stage to

industrial implementation

J.W. Jurewicz, M.I. Boulos,

Tekna Plasma Systems Inc.

2935 boul. Industriel, Sherbrooke, Qc, Canada J1L 2T9

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Outline

• Presentation of Tekna Advanced Materials• Risk Management Process• Design Considerations• Plasma Processing Units• Building Infrastructure• Safety Barriers System • Conclusion

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Tekna Advanced Materials Inc.• The mission of Tekna Advanced Materials Inc. (TAM) is to

develop and commercially manufacture high added value advanced materials using thermal plasma technology.

• There is an increasing demand for powders at the micron, sub-micron and nano-sized (< 100 nm) level for a wide range of applications varying from microelectronic, to the biomedical and the cosmetic industry.

• Intensive research effort is dedicated to the assessment of the potential hazard that nano-sized materials can have on human health. These materials have to be handled with utmost care and well defined procedures in order to minimize the chances of human exposure.

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Tekna Advanced Materials Inc.

This paper explains the approach undertaken by Tekna engineers to design, built and run a viable operation for the commercial production of advanced materials including nanostructered materials and powders.

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Outline

• Presentation of Tekna Advanced Materials

Risk Management Process

• Design Considerations• Plasma Processing Units• Building Infrastructure• Safety Barriers System • Conclusion

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Risk Management Process [1]

6[1] “Risk management – Principles and guidelines on implementation”, IEC/ISO 31000:2009 –

CAN/CSA-IEC/ISO 31000-10 (2010)

Accident Sequence[2]

← THE ACCIDENT SEQUENCE →Normal condition Initial phase Concluding phase Injury phase

▲ ▲ ▲ Lack of control Loss of control Energy/Toxicity exposure

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[2] Sklet S., “Safety barriers: Definition, classification and performance”, J. Loss Prevention in the Process Industries, 19, pp. 494-506 (2006)

Accident Sequence & Principle of Barriers[2]

← THE ACCIDENT SEQUENCE →Normal condition Initial phase Concluding phase Injury phase

▲ ▲ ▲ Lack of control Loss of control Energy/Toxicity exposure

PREVENT PROTECT

PREVENT CONTROL MITIGATE

AVOID PREVENT CONTROL PROTECT

Barriers generic functions of process safety management

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Principle of Barriers[2]

• Safety barriers are physical and/or non-physical means planned to prevent, control, or mitigate undesired events or accidents

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Process Safety Management [2]

Risk

1

Risk identification and its characteristics /

parameters

3

Identification and

impositionof barrier to reduce the frequency and/or the

consequence of a failure

4Is barrierefficiency

acceptable?

NO

YES

Acceptationof residual risk

Identification of possible system’s

failure and its characteristics

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Nano-Materials (NM) Risk Assessment Uncertainty*

.....On the whole, a consensus is beginning to emerge,

risk assessment for chemical should be appropriate for NM,

but

they most likely need some methodological modifications.

Exactly what modifications are needed is not consistently made clear, and how long it will take to make these modifications is not often stated......

11* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol.

12, 2, pp. 383-392 (2010)

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Process Safety Management [2]

Risk

1

Risk identification and its characteristics /

parameters

Nano-Materials (NM) Risk Assessment Uncertainty*

Concerning Risk Assessment:

.....However, how long will this [Risk Assessment] process take especially given the diversity of NM and applications ?

A recent analysis estimates that testing existing nanoparticles in the USA alone will

cost between $249 million and 1,18 billion and

take 34-53 years for completion.

13* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol.

12, 2, pp. 383-392 (2010)

Nano-Materials (NM) Risk Assessment Uncertainty

..... In some cases, the precautionary principle has been invoked to support decisions in the absence of full scientific certainty......[*]

Conclusions[**]

……Presently, quantitative health hazard and exposure data are not available for most nanomaterials. Therefore, health risk evaluation for the workplace currently relies to a great degree on professional judgments for hazard identification, potential exposures and the application of appropriate safety measures

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* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol. 12, 2, pp. 383-392 (2010)

**ISO/TR 12885, “Nanotechnologies – Health and safety practices in occupational settings relevant to nanotechnologies”, pp. 1-79 (2008)

Outline

• Presentation of Tekna Advanced Materials

• Risk Management Process

Design Considerations

– Hazards’ parameters

– Hazard evaluation by control banding

– Efficiency of risk management strategies

• Plasma Processing Units

• Building Infrastructure

• Safety Barriers System

• Conclusion

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The nano-particles are characterized (among others) by their very high specific surface area which is the origin of their high reactivity leading to both pyrophoric properties for combustible materials and/or to toxicity to humans.

The pyrophoric properties may be attenuated by:– Passivation process - formation of a controlled thickness

oxide layer over the particle surface;– Encapsulation process – formation of thin layer of

secondary material (like carbon or polymer) over an entire surface of particle;

– On-line wet collection of nano-powder in an inert liquid;

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The toxicity parameters include the dose (effective, toxic and lethal) and the time of exposition.

The risk management program should aim at both minimizing the dose and shortening time and/or frequency of exposition.

The possible ways to minimize the dose are (among others):– handling the nano-particles in tightly closed

environment (as long as possible) and – use the local ventilation for the case where the products

have to be handled in open atmosphere.

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Design Considerations – Hazard Evaluation

S.Y.Paik et all.[3] considers two categories of hazard evaluation: severity and probability of exposure to nanomaterials.

As the severity is mainly material dependant, this parameter was treated as generic without particular identification during the initial stage of project.

The probability of exposure is strongly process design dependant and as such was the principal guiding parameter during the conception stage of the entire operation.

[3] Paik S.Y., D.M. Zalk, P. Swuste, “Application of a Pilot Control Banding Tool for Risk Level Assessment and Control of Nanoparticle Exposure”, Ann. Occup. Hyg., Vol. 52, No 6, pp. 419-428 (2008)

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Design Considerations – Hazard Evaluation Probability of Exposure [3]

Parameter Points

Estimated amount of nanomaterial [mg]

> 100 11-100 0-10 Unknown

25 12,5 6,25 18,75

Dustiness / MistinessHigh Medium Low None Unknown

30 15 7,5 0 22,5

Number of employee with similar exposure

> 15 11-15 6-10 1-5

15 10 5 0

Frequency of operationDaily Weekly Monthly Less than

monthlyUnknown

15 10 5 0 11,25

Duration of operation> 4 h 1-4 h 30-60 min < 30 min Unknown

15 10 5 0 11,25

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Design Considerations – Hazard Evaluation Probability of Exposure [3]

Parameter Points

Estimated amount of nanomaterial [mg]

> 100 11-100 0-10 Unknown

25 12,5 6,25 18,75

Dustiness / MistinessHigh Medium Low None Unknown

30 15 7,5 0 22,5

Number of employee with similar exposure

> 15 11-15 6-10 1-5

15 10 5 0

Frequency of operationDaily Weekly Monthly Less than

monthlyUnknown

15 10 5 0 11,25

Duration of operation> 4 h 1-4 h 30-60 min < 30 min Unknown

15 10 5 0 11,25

Material Pending Values aimed at during design20

Efficiency of Risk Management Strategies [4]

[4] C. Ostiguy, B. Roberge, L. Ménard, C. Endo, “ Best Practices Guide to Synthetic Nanoparticle Risk Management”, Studies and Research Projects, Report R-599, IRSST (2009) 21


All above mentioned risk management strategies were analysed in the light of existing hazard management approach as offered by Tekna Plasma Systems Inc. in commercial plasma processing units.

It was decided to apply bottom-up design method to build up the commercial production facility by adding additional layers of protection / prevention to already existing ones.

At the same time, the economic aspects and processing costs reduction have been addressed as well.

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Processing Costs Reduction Strategies

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Outline

• Presentation of Tekna Advanced Materials• Risk Management Process• Design Considerations

Plasma Processing Units– Spheroidization Unit– Nanopowders Synthesis Unit

• Building Infrastructure• Safety Barriers System• Conclusion

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Plasma Processing Unit – Spheroidization

Some of the typical characteristics of Tekna’s commercial induction plasma processing unit

• Continuous operation 24/5-7 including raw material feeding, product cooling & withdrawal - the latter ones are done pneumatically under controlled processing atmosphere;

• All plasma processing operations are automated (including plasma ignition) through in-house conceived computer programme with up to 5 levels of alarms (if required by process safety);

• Deflagration containment design.

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Continuous liner packing to replace the glove box

Nano-Powders Synthesis1 Plasma Torch

2 Plasma Reactor

3 Filter

4 PneumaticTransfer Unit5 Glove Box

Outline

• Presentation of Tekna Advanced Materials• Design Considerations• Plasma Processing Units

Building Infrastructureo Cooling Water Systemo Washing / Rinsing Water Systemo Ventilation System

• Safety Barriers System • Conclusion

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Cooling Water System

• Total power to be dissipated – 2,5 MW

• Dissipation method : space (building) heating during cold season prior towater evaporation in cooling tower;

• Cooling water exit temperatureis kept constant by controllingfan speed through a frequencydrive;

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Cooling Water System – Impurities Control

Suspended and/or dissolved solids control:

• Cooling water origin: – Primary water intake – rain water / melted snow collected

in 28 m3 water tank from the roof of an entire building - (no dissolved solids – weak charge of suspended solids)

– Secondary water intake – city water originating from Memphremagog lake (weak charge of dissolved solids, no suspended solids)

• Solid particles collected from dust laden outside air by cooling water - the water tank design allows them to sediment at bottom collection well

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• Biological charge growth is controlled by intensive (> 40000 µWs/cm2) UV irradiation of cooling water in closed loop circuit

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Leak of materials from plasma processing system – no possibility due to mechanical isolation of primary DI water loop from cooling water loop through stainless heat exchanger – water quality (resistivity) is monitored

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HEAT EXCHANGER

PUMP 1COOLING WATER

COOLING TOWERDOUBLE WALL

REACTOR

P-1

P-3

P-4

PUMP 2DI WATER

P-5

RESIST

P-7

FEED

PRODUCTS

P-8

P-9

P-6


Cooling water is free of corrosion prevention chemicals (the entire cooling system is either of polymer or stainless steel origin) allowing to dispose the excess of rain water into environment without manmade contaminants.

The solids collected from outside air as sediments at the bottom collection well are evacuated periodically

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Washing / Rinsing Water System

Among procedures to minimize the exposition to nano-sized particulates, the wet collection/cleaning of reactor’s interiors as well as possible spills is strongly recommended.

The production halls are equipped (among others) with gray and deionized (DI) water distribution systems.

• The gray water serves as washing fluid for all plasma processing interiors during their periodic cleaning or when changing the treated materials; the powder laden water is then evacuated through sub-floor conduits to one of the collecting tanks where it is left for solids decantation and subsequent treatment; similarly, in the case of materials spill on the floor, the leftovers are washed down by city water and evacuated to the same collecting tank;

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Washing/Rinsing Water System

• The DI water serves as final rinsing water as well as safety shower water – for such application the water has to be kept lukewarm.

This water is constantly treated by UV radiation to prevent bacterial growth - similarly to the cooling water circuit.

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Local Ventilation System

Designing Considerations :

•Design according to the standard ANSI/AIHA Z9.2 – 2006 – «Fundamentals Governing the Design and Operation of Local Exhaust Ventilation Systems»

•Exhausted air leaving premises has to be cleaned to HEPA standard (99,97 % of arrestance) through progressive retention of particles through a sequence of filters with increasing arrestance to avoid rapid clogging of a final filter

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Local Ventilation System

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MERV = Minimum Efficiency Reporting Value

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Plasma Processing Hall – Spheroidization

HEPA Filter

Pre-Filter& Primary Filter

Ventilation System

• Pre-filter and primary filter are housed in one box and are fed from 2 exhaust arms;

• Each final filter (HEPA) collects spent air from 2-3 primary filters;

• Both primary and final filters’ pressure losses are monitored locally (gauge) and remotely (control room) – an operator is aware of the actual pressure loss value and a visual and audio alarms are set as well;

• The exhaust fan (located over the roof) is driven by a frequency controlled drive allowing to maintain constant air evacuation rate in spite of increasing pressure losses in the chain of filters – in the case of an emergency, the evacuation rate increases automatically to its maximal value.

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Outline

• Presentation of Tekna Advanced Materials• Risk Management Process• Design Considerations• Plasma Processing Units• Building Infrastructure

Safety Barriers System– Example: Flammability hazard– Example: Nanoparticles spill hazard

• Conclusion

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Safety Barriers System - Examples

• Hazard – Flammability of processing gases/products:– Hydrogen in-situ production rate follows its consumption – no

stocking– PLC activated vacuum/pressure inerting of processing vessels

including air lock charged with powdered raw material and feeder hoper for each charging operation;

– Monitoring of residual oxygen concentration in processing vessels;

– Controlled passivation of pyrophoric products;– Stocking of pyrophoric products under inert atmosphere;– Equipment designed to withstand deflagration;– Process off gas (already saturated with inerting water vapour)

is exhausted to outside through the flash arrestor;

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Safety Barriers System – Nano-Particles Leak

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Safety Barriers System

• Air lock exit from production hall

• Personal Protection Equipment

Motorized air blower unit equipped with splash protected gas, vapour & particulates (HEPA class) filtering unit

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Outline

• Presentation of Tekna Advanced Materials• Risk Management Process• Design Considerations• Plasma Processing Units• Building Infrastructure• Safety Barriers System

Conclusion

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Conclusion (1)

The bottom-up design approach from Tekna built standard thermal plasma processing units to entire production facility allowed to address and successfully resolve all major safety and economic issues involved with the production of advanced nano-sized materials by:

Conceiving multiple – level barriers against Nano-Particle spill hazard;

Minimizing the frequency of exposure to hazardous materials through (among others) high level of process automation including final products packaging and separate production halls for higher hazard level materials;

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Conclusion (2)

• Establishing and implementing the adequate operational procedures;

• Cooling water cost reduction by recovery of rain / snow;• Space heating by spent heat from plasma processing units;• Minimizing the waste disposal costs through in-house

recycling procedures and elimination of water conditioning chemicals (replaced by UV radiation);

• On-site, consumption regulated, production of hydrogen;• Recycling (after conditioning) the major part of consumed

gas; • Optimizing the production rate of each product according to

its specifics.

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Acknowledgments

Tekna Plasma Systems Inc.

• Loïc Brochu• Jean-Pierre Crête• Nicolas Dignard• David Héraud• François Hudon

Institute de recherche Robert Sauvé en santé et en sécurité du travail

• Claude Ostiguy

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Tekna Plasma Systems Tekna Advanced Materials

THANK YOU

Jerzy Jurewicz & Boulos_Analysis of safety aspects associated with the plasma synthesis and handling...

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