E SC 412Nanotechnology: Materials, Infrastructure, and Safety

Wook Jun Nam

Outline

• General Safety Awareness

• Wet Chemistry Safety

• Gas Safety

• Biological Safety

• Nanomaterial Safety

• Energy Safety

• Environmental Concerns

General Gas Concerns

• Generally speaking, the gases used in nanofabrication and synthesis are contained in heavy steel cylinders, under high pressure.

– If the valve on the cylinder is damaged, the cylinders can take off like rockets.

• The cylinders are heavy and can cause physical damage to a person if dropped.

General Gas Concerns

• The cylinders containing gases that pose a health hazard are kept in special exhaust cabinets, equipped with alarms while in use.

Gas Cabinet With Exhaust

Cylinder Storage

• When being stored, gas cylinders must be securely fastened to a bracket.

Transporting Cylinders

• When being transported, the cylinders must be equipped with a valve cap and be transported in a safety cart.

cart

safety strap

valve covercap

General Gas Concerns

• Toxic gas alarm systems must be installed where toxic gasses are used.

• These alarms must be calibrated to sound when chemical fumes, even when well below dangerous exposure levels, are detected.

• If the alarm does sound, it is necessary to exit the laboratory immediately.

Toxic Gas Alarm and Strobe Light

Pyrophoric Materials

• Materials that ignite spontaneously in air at, or below 54.4 °C (130 °F)

• Common pyrophoric nanofabrication materials include:

– Silane (SiH4)

– Disilane (Si2H6)

– Phosphine (PH3)

– Diborane (B2H6)

Silane• A colorless gas used as a silicon source in

numerous fabrication processes.

• Silane will readily decompose at atmospheric pressure:

SiH4 (g) Si (g) + 2H2 (g)

• Silane’s constituents react with atmospheric oxygen, undergoing a very energetic redox reaction, forming silica (SiO2) and water:

Si (g) + O2 (g) SiO2 (s) 2H2 (g) + O2 (g) 2H2O (g)

Oxidized Reduced Oxidized Reduced

Phosphine

• One of the most toxic substances in the fab, it is colorless gas with an odor of rotting fish.– Used as a dopant source during ion implantation.

• Like silane, it is pyrophoric.

• If inhalation occurs, phosphine causes:– Coughing, Nausea, Burning sensations in the diaphragm,

Diarrhea, Abdominal pain, Headache, Dizziness, Ataxia (nervous system damage), Pain and tightness in the chest, Tremors, Shortness of breath, Vomiting, and Convulsions.

Asphyxiates

• Even seemingly inert chemicals such as nitrogen gas, can pose a threat.

• Nitrogen gas is considered an asphyxiate, meaning that it can displace/dilute the oxygen in the atmosphere of confined spaces.

• If inhaled in large enough quantities, asphyxiation occurs leading to death.

Gas Concerns

• Some gas byproducts are dangerous and cannot be released into the environment.

• A common solution is to “scrub” or clean up this byproduct.

• This section will examine common methods to clean gas byproducts.

Environmental Concerns

• Wet scrubbers

– Use solvents to adsorb the chemicals that are in the gaseous mixture or liquid mixture.

– These chemicals can be recycled or reused because of the processing method that is used.

– Problem may be disposal, and monitoring the reactant material.

– Many kinds of scrubbers on the market today.

Basic Scrubber

Contaminated

(dirty) gas inlet

Corrosive rated pump Scrubber 1Scrubber 2

Fan

To Atmosphere

Scrubbers

• Spray-tower wet scrubber– Uses a slurry method to

remove contaminates.

– Able to remove organic, inorganic, and particulate matter.

– Is able to recycle solvents.

http://www.epa.gov/eogapti1/module6/matter/control/control.htm

Scrubbers

• Spray-tower wet scrubbers

– How they work?

• Mixes the solvent with the gas that is being purified.

• The gas flows upward into wires.

• These wires condense the vapor into liquid.

• This liquid is then deposited onto the bottom.

• This slurry is the processed or removed.

ScrubbersSpray-tower Scrubbers

Some Advantages

1. Relatively low pressure drop.

2. Can handle flammable and explosive dust with little risk.

3. Fiberglass-reinforced plastic construction permits operation in highly corrosive atmosphere.

4. Relatively low purchase cost

5. Relatively free from plugging.

6. Relatively small space requirements.

7. Ability to collect PM as well as gases.

Some Disadvantages

1. May create water or liquid disposal problem.

2. Waste product collected wet.

3. Relatively low mass-transfer efficiencies.

4. Relatively inefficient at removing fine particulate matter.

5. Is sensitive to temperature changes.

6. Relatively high operating cost.

Scrubbers

• Condensation scrubber

– This scrubber operates by making particulate matter larger.

– Used for primarily fine particle matter.

Condensation Scrubber

Some Advantages

1. Can handle flammable and explosive dust with little risk.

2. Can handle fine particulate matter.

3. Collection efficiency can be varied.

4. Corrosive gases and dust can be neutralized.

Some Disadvantages

1. Effluent liquid can create water pollution problems.

2. Product collected wet.3. High potential for corrosion

problems.4. Protection against freezing

required.5. Off-gas require reheating to avoid

visible plume.6. Collected particulates may be

contaminated, and may not be recyclable.

7. Disposal of waste sludge may be very expensive.

Outline

• General Safety Awareness

• Wet Chemistry Safety

• Gas Safety

• Biological Safety

• Nanomaterial Safety

• Energy Safety

• Environmental Concerns

Biological Safety

• Biological safety is implemented to ensure the safe and proper use of biohazardous materials.

• Proper training on materials and work practices must be performed.

The 1,2,3’s of Bio Safety Levels

• Bio safety levels (BSL) were developed for

laboratories to provide increased personal and

environmental protection, needed when

biological materials and reagents are used.

• BSL-1: appropriate for working with agents that do

not cause disease.

• BSL-2: appropriate for working with agents that pose

a moderate risk to personnel or the environment.

• BSL-3: appropriate for working with infectious agents

can cause serious disease or death.

• Current safety information is available from

OSHA, and can be accessed on the internet.

Outline

• General Safety Awareness

• Wet Chemistry Safety

• Gas Safety

• Biological Safety

• Nanomaterial Safety

• Energy Safety

• Environmental Concerns

Nanomaterial Safety

– Nanotechnology is an emerging field. As such, there are many uncertainties as to whether the unique properties of engineered nanomaterials (which underpin their commercial and scientific potential) such as nanoparticles also pose occupational health risks.

– The Food & Drug Administration has yet to distinguish nanomaterials such as nanoparticles as being a separate and different substance than their bulk source.

– Nanomaterials can have different properties than bulk materials. MSDS sheets are generally written for bulk properties.

– At this time clear and concise rules for nanomaterial safety are under development by government agencies.

Nanomaterial Safety

The U.S. government through a joint effort of Department of Heath and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health has published a cohesive set of guidelines and procedures for nanomaterials. The notes in this section reflect this document.

Approaches to Safe Nanotechnology: Managing the Health and Safety Concerns Associated with Engineered Nanomaterials

http://www.cdc.gov/niosh/docs/2009-125/

Nanomaterial Safety

An additional reference is also available from the European Agency for Safety and Health at Work

Workplace exposure to nanoparticles

http://osha.europa.eu/en/publications/literature_reviews/workplace_exposure_to_nanoparticles

Nanomaterial Safety

– Workplace practice

• Since nanomaterials are fairly new, regulations concerning them have yet to be complete.

• Controls and policies are under development for nanofabrication uses and nanoparticle types.

• Many unknowns about short and long term exposures and limits have to be examined.

• Until further information is available, interim safe working practices should be used based on the best available information.

Nanomaterial Safety

EPA: Environmental Protection Agency

• EPA is leading scientific efforts to understand the potential risks to humans, wildlife, and ecosystems from exposure to nanomaterials – those materials produced at the nano scale.

• Scientists are studying the unique properties of nanomaterials, determining their potential impacts, and developing approaches to evaluate any risks.

• They are also exploring how nanomaterials can be used effectively to clean up contaminants released into the environment.

www.epa.gov/nanoscience

Nanomaterial Safety

Focus of EPA Nanotechnology Research

• Identifying sources of nanomaterials and how they are transported through the environment to their destination (fate and transport) and how people may be exposure to nanomaterials.

• Understanding human health and ecological effects to assist with conducting risk assessments and development of scientific methods to help with risk assessments

• Developing risk assessment approaches that can be used in decision making to identify and evaluate potential risks of nanomaterials

• Preventing and mitigating risks of nanomaterials in the environment

www.epa.gov/nanoscience

Nanomaterial Safety

EPA Research Interests

www.epa.gov/nanoscience

Nanomaterial Safety

• Nanomaterials have the greatest potential to enter the body through the respiratory system as nanoparticles

• They may also come into contact with the skin or be ingested. A variety of exposure paths are possible

– These exposures may be short or long term events

– Based on results from human and animal studies, airborne nanoparticles can be inhaled and deposit in the respiratory tract; and based on animal studies, nanoparticles can enter the blood stream, and translocate to other organs.

Nanoparticle Safety

• Ultra fine particles may cause respiratory disease and even some types of cancers. Heart diseases and central nervous system problems have been associated from nanoparticle contamination in the body.

– A 1 µm particle weighs 1,000,000 times more than a 10nm particle. Since the mass of the nanoparticle is so small, these particles can stay suspended in the air for a long time and may behave like a gas.

– These particles may enter the lungs, skin and eyes.

Nanoparticle Safety

• The following workplace tasks can increase the risk of exposure to nanoparticles:

– Working with nanomaterials in liquid media without adequate protection (e.g., gloves)

– Working with nanomaterials in liquid during pouring or mixing operations, or where a high degree of agitation is involved

– Generating nanoparticles in non-enclosed systems

– Handling (e.g., weighing, blending, spraying) powders of nanomaterials

Nanoparticle Safety

• The following workplace tasks can increase the risk of exposure to nanoparticles: (Con’t)– Maintenance on equipment and processes used to produce or

fabricate nanomaterials and the cleaning-up of spills and waste material containing nanomaterials

– Cleaning of dust collection systems used to capture nanoparticles

– Capturing debris from machining, sanding, drilling, or other mechanical disruptions of materials containing nanoparticles

Nanoparticle Safety Precautionary Measures• For most processes and job tasks, the control of airborne exposure

to nanoaerosols can be accomplished using a variety of engineering control techniques similar to those used in reducing exposure to general aerosols.

• The implementation of a risk management program in workplaces where exposure to nanomaterials exists can help to minimize the potential for exposure to nanoparticles. – Evaluating the hazard posed by the nanomaterial based on

available physical and chemical property data, toxicology, or health-effects data

– Educating and training workers in the proper handling of nanomaterials (e.g., good work practices)

Nanoparticle Safety Precautionary Measures (con’t)• Establishing criteria and procedures for installing and evaluating

engineering controls (e.g., exhaust ventilation) at locations where exposure to nanomaterials might occur

• Developing procedures for determining the need for and selecting proper personal protective equipment (e.g., clothing, gloves, respirators)

– No guidelines are currently available on the selection of clothing or other apparel (e.g., gloves) for the prevention of dermal exposure to nanoaerosols. However, some clothing standards incorporate testing with nanometer-sized particles and therefore provide some indication of the effectiveness of protective clothing

• Systematically evaluating exposures to ensure that control measures are working properly and that workers are being provided the appropriate personal protective equipment

Nanomaterial Safety • Cleanup and disposal of nanomaterials

– No specific guidance is currently available on cleaning up nanomaterial spills or contamination on surfaces

– Recommendations developed in the pharmaceutical industry for the handling and cleanup of pharmaceutical compounds might be applicable to worksites where engineered nanomaterials are manufactured or used

– Standard approaches for cleaning powder spills include using HEPA-filtered vacuum cleaners, or wiping up the powder using damp cloths or wetting the powder prior to dry wiping.

– Liquid spills are typically cleaned by applying absorbent materials/liquid traps.

– Drying and reusing contaminated cloths can result in re-dispersion of particles.

– Energetic cleaning methods such as dry sweeping or the using of compressed air should be avoided or only used with precautions

Nanoparticle Safety • Effects Seen in Animal Studies

– Experimental studies in rats have shown that at equivalent mass doses, insoluble ultrafine particles are more potent than larger particles of similar composition in causing pulmonary inflammation, tissue damage, and lung tumors

– [Lee et al. 1985; Oberdörster and Yu 1990; Oberdörster et al. 1992, 1994a,b; Heinrich et al. 1995; Driscoll 1996; Lison et al. 1997; Tran et al. 1999, 2000; Brown et al. 2001; Duffin et al. 2002; Renwick et al. 2004; Barlow et al. 2005].

– These studies have shown that for poorly-soluble low toxicity particles, the dose-response relationships are consistent across particle sizes when dose is expressed as particle surface area.

– In addition to particle size and surface area, studies have shown that other particle characteristics can influence toxicity. Reactive oxidant generation on the particle surface is an important factor influencing lung response to particles

– Studies indicate that for nanoparticles with similar properties the toxicity of a given mass dose will increase with decreasing particle size due to the increasing surface area.

Nanoparticle Safety • Effects Seen in Animal Studies

– Carbon nanotubes (CNT) are nanoparticles. They are engineered nanomaterials that may have increased production and use

– Studies have shown that the toxicity of CNT may differ from that of other nanomaterials of similar chemical composition.

– Single-walled CNTs (SWCNT) have been shown to produce adverse effects including granulomas in the lungs of mice and rats at mass doses at which ultrafine carbon black did not produce these adverse effects.

– While both SWCNTs and carbon black are carbon-based, SWCNTs have a unique, fibrous structure and a unique surface chemistry. They offer excellent electrical and strength properties.

– Recent studies point to the hypotheses that CNTs may behave like asbestos.