HIGHLY REACTIVE MATERIALS, HIGH-PRESSURE REACTIONS, OR VACUUM SYSTEMS FACT SHEET

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Northwestern UniversityVice President for Research Chemical and Biological Safety Committee Office for Research Safety 

Based on 29 CFR 1910.1450, Occupational exposure to hazardous chemicals in laboratories, by reference to Prudent Practices in the Laboratory, National Research Council. 

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GENERAL OPERATIONAL PRACTICES FOR REACTIVE/EXPLOSIVE HAZARDS/SYSTEMS 

Note: There may be overlap between these categories. Compounds may be reactive, may cause system overpressurization, and may be used with vacuums. All three areas (highly reactive materials, high-pressure systems, vacuum systems) may apply to one reaction. 

1. Heat guns are not used for heating if flammable vapors are present. Instead, heating tapes, mantles, or water, steam, or oil baths are used. 
2. If an explosion were to occur, provisions have been made to contain the entire reaction mixture. 
3. Dry ice solvent baths are not used for reactive gases. 
4. Hot liquids are not brought into sudden contact with lower-boiling liquids. 
5. Boiling chips are not added once the heated liquid has exceeded its boiling point. 
6. The areas where highly reactive chemicals, high-pressure, or vacuum equipment are used are posted with signs to warn colleagues of potential danger. 
7. When a reaction becomes uncontrollable, heat is removed, the addition of reagents is suspended, nearby lab workers are notified, and the chemical fume hood sash is closed until the temperature has dropped. 
8. When a potentially hazardous reaction is attempted, total quantities of reactants are limited to 0.5 g in the reaction vessel. 
9. Emergency equipment is on hand for reactions that could runaway violently. 
10. When appropriate, tongs are used to manipulate highly reactive chemicals to prevent exposure of any part of the body to possible injury (e.g., when immersing sodium metal in solvents, handling heated crucibles, or removing weighing dishes from ovens). 

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HIGHLY REACTIVE MATERIALS 

A. Definition. Highly reactive materials are those agents that undergo rapid chemical change causing exothermic or other self-accelerating reactions when subjected to heat, impact, friction, light, catalysts, or other initiation. These agents are materials that will detonate or deflagrate. Highly reactive materials encompass (but are not limited to): 

• Air-reactive chemicals (e.g., palladium or platinum on carbon, platinum oxide, Raney nickel) 
• Metal hydrides (e.g., lithium aluminum hydride, sodium borohydride) 
• Cryogenic materials/liquefied gas, supercritical fluids (e.g., oxygen, nitrogen, helium) 
• Highly water-reactive chemicals (e.g., aluminum bromide, metal hydrides, phosphorus pentachloride, tin tetrachloride, titanium tetrachloride) 
• Explosive dusts (e.g., magnesium powder, zinc dust, carbon powder, flowers of sulfur) 
• Explosives, other (e.g., diazomethane, hydrogen peroxide, hydrogen, chlorine, polymerizing acrolein, trinitrotoluene) 
• Organic peroxides (e.g., acetyl peroxide, benzoyl peroxide) 
• Organometallic chemicals and active metals (e.g., trimethyl gallium; sodium, magnesium, lithium, potassium) 
• Oxidizing agents (e.g., halogens, oxyhalogens, peroxyhalogens, permanganates, nitrates, chromates, persulfates, peroxides) 
• Perchloric acid and perchlorates (e.g., sodium perchlorate) 
• Peroxide-forming chemicals (e.g., acrylonitrile, dioxane, ether, isopropanol, tetrahydrofuran) 
• Polymerization reactions (e.g., acrylate monomers) 
• Polynitro organic chemicals (e.g., picric acid, dinitrophenylhydrazine, methyl nitronitrosoguanidine) 
• Pyrophoric chemicals (e.g., boranes, white phosphorus, alkyl metals such as n-butyllithium and dibutyl magnesium) 
• Shock-sensitive and other unstable chemicals (e.g., acetylides, azides, nitro compounds, organic nitrates, perchlorates). 

Note: Many of the above classes of materials overlap with other classes (e.g., organometallics may be pyrophoric). The list is intended merely to provide guidance for determining whether this section applies to the research in your lab. Exact classification is not necessary. 

B. Operational Practices For Specific Classes Of Reactives. The categories listed below are not exhaustive and do not necessarily cover all possible circumstances that must be controlled. 

Cryogenic materials 

1. Cryogenic materials are not warmed in closed containers. 
2. Relief devices have been engineered into the containers or closed systems. 
3. Dewars are inspected for ice plug formation. 
4. Dry leather or other impervious thermal gloves are worn to prevent burns. Potholders may be used to handle cryogenic containers. 
5. Cryogenic materials are not used in a confined space with inadequate ventilation due to the potential for asphyxiation. 
6. Transfers of materials are conducted very slowly to minimize boiling and splashing. 

Explosive dusts 

1. Suspensions of oxidizable particles are handled wet. 
2. The airborne particulates are not exposed to ignition sources. 
3. Adequate ventilation has been provided to control the concentration of airborne dusts. 

Organometallics and pyrophoric chemicals 

1. Where organometallics are used, Class D fire extinguishers or pails of dry powder extinguishing agent or sand are provided. 
2. All pyrophorics are used and stored in an inert atmosphere (e.g., under nitrogen or argon). 
3. Regulators are set correctly to prevent glassware from being overpressurized with nitrogen or argon. 
4. To avoid spills resulting in fires, breakable glass bottles are stored inside a rubber or plastic bottle carrier. 

Organic peroxides and peroxide-forming solvents 

1. Organic peroxides and peroxide-forming solvents are protected from and stored away from light. 
2. Ceramic, plastic, or wooden spatulas are used with organic peroxides. Metal spatulas are never used. 
3. Glass containers with screw caps or glass stoppers are not used with organic peroxides. 
4. Friction, grinding, or other forms of impact are not permitted near peroxides. 
5. Organic peroxides are diluted with inert solvents such as mineral oil to reduce their sensitivity to heat and shock. 
6. Liquid organic peroxides are never allowed to freeze, as phase changes increase the sensitivity of these compounds to shock and heat. 
7. Peroxide-forming solvents are checked for the presence of peroxides prior to heating of the solvent and after each month of storage. Testing may be conducted with instantaneous peroxide indicator strips. 
8. Peroxide-forming solvents are disposed of through ORS within six months after opening. 
9. Peroxide-forming compounds are stored in a cool, dark, well-ventilated area. 

Ether used as an anesthetic 

1. Like other peroxide-formers, ether must be stored in a cool, dry, well-ventilated place, out of direct sunlight. It must be purchased in small containers, no more than is absolutely necessary. It shall be stored as far back on a shelf as possible to minimize the potential for falling. It should be easy-to-reach to prevent knocking against the container. 
2. Ether is checked for peroxides monthly or discarded six months after opening. Peroxide test strips are available from Lab Safety Supply and other reputable safety supply distributors (e.g., Fisher, Baxter). In compliance with University safety policy, a chart of test results accompanies the container of ether. It may be posted on the storage area or kept on a clipboard. Information regarding the chart and test strips is available from ORS. A lab safety designate has been assigned responsibility for regular peroxide testing. 
3. Both unused ether supplies (older than 6 months) and ether known to contain peroxides must be disposed of through ORS. Evaporation of ether in a chemical fume hood is forbidden by law, except for residual amounts in an empty can. Disposal down the drain is also unlawful. 
4. Animal carcasses containing ether are stored in explosion-safe refrigerators or freezers where ether vapors cannot ignite. 

Oxidizing agents 

1. Oxidizing agents are separated from reducing materials, metals, and ordinary combustibles. 
2. Oil baths are not used when oxidizing agents are present. 

Perchloric acid and perchlorates 

1. Organic materials are digested with nitric acid before the addition of perchloric acid. 
2. Perchloric acid is heated (i.e., during acid-based digestion) only in a water-washdown laboratory chemical fume hood of noncombustible construction. 
3. Chemical fume hoods in which perchloric acid is heated are inspected frequently for the accumulation of perchlorates. Deposits are saturated with water and removed. 
4. Perchloric acid is never used near, nor stored on, wooden shelves. 
5. Perchloric acid is stored in glass bottles on noncombustible (e.g., ceramic or plastic) trays large enough to contain the entire contents of the bottle. 
6. Perchloric acid and perchlorates are never stored with organic materials. 
7. Perchloric acid is never heated with sulfuric acid. 

Polynitro organic chemicals and shock-sensitive or unstable compounds 

1. The stock of polynitro compounds is stored separately from other lab chemicals. 
2. Stock is regularly inspected for degradation or dehydration, as these compounds may become more shock-sensitive with age. 
3. Polynitro compounds are disposed of through ORS when no longer needed. They are not placed in storage for future use, as they may become more hazardous over time. 
4. When polynitro and shock-sensitive compounds are moved, they are handled by the container bottom and never by the cap or lid. 
5. Picric acid is hydrated or kept in solution to reduce sensitivity. It is never allowed to dry out completely. 
6. Solid sodium azide, in quantities above 25 g, is dissolved when it arrives in the lab. Solutions of sodium azide do not pose the danger of shock-sensitivity associated with the solid form; however, the hydrazoic acid generated when the azide is dissolved is extremely toxic. Therefore, the solution is always prepared inside a chemical fume hood. If not dissolved, solid azide must be stored in a locked cabinet. 
7. Teflon or other nonmetal spatulas are used with solid sodium azide due to its reactivity with metals. 

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HIGH-PRESSURE SYSTEMS 

A. Definition. High-pressure reactions are those experiments that are carried out at pressures above one atmosphere. This includes most hydrogenation reactions since explosive oxygen-hydrogen mixtures can be formed as a result of these reactions. 

B. Operational Practices. 

1. A label on each pressure vessel indicates the maximum allowable working pressure and temperature. 
2. Service lines are not connected to any closed apparatus incapable of withstanding the maximum pressure of the service line (air, water, etc.). 
3. All pressure systems are protected with appropriate pressure-relief devices. 
4. The pressure-relief device is installed so that the discharge is directed away from the area where a person could be affected. 
5. Pressure-relief devices are inspected periodically. Orifices on both sides of the pressure-relief device are checked for obstruction. 
6. The lab workers use pressure gauges with pressure ranges about twice the working pressure of the system. 
7. Containers, fittings, and other equipment to be used when working with pressure vessels are able to withstand the stresses imposed by the given pressures and temperatures. 
8. Vessels containing solution are not filled above capacity; preferably, the vessel is only half full. 
9. The pressure levels of high-pressure devices are monitored periodically as heating proceeds. 

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VACUUM SYSTEMS 

A. Definition. Vacuum systems include those activities involving mechanical vacuum pumps, building vacuum systems, water aspirators, or steam aspirators. 

Work with vacuum systems poses a substantial danger of injury to the operator from flying glass shrapnel released during an implosion. Other hazards may include: 

• the toxicity of the chemicals in the vacuum system 
• fire following breakage of a flask containing flammable solvents 
• toxicity from the mercury in manometers and gauges 
• over- or under-pressurization arising with thermal conductivity gauges 
• electric shock with hot cathode ionization systems. 

B. Operational Practices. 

Vacuum apparatus 

1. Vessels used in vacuum operations are protected with suitable relief valves (vacuum breaker). 
2. A protective shield is placed around evacuated systems. 
3. Lab workers wear safety glasses and face shields when working with evacuated systems or setting up such systems. 
4. The vacuum system has been arranged to allow the equipment to be moved without transmitting strain to the neck of the flask; flasks are supported from below as well as by their necks. 
5. The vacuum apparatus is well out of the way of traffic to avoid being struck inadvertently. 
6. Belt-driven mechanical pumps have been equipped with protective guards to enclose the moving belts. 

Capture of contaminants 

1. Each vacuum system used for solvent distillation operations is protected by a suitable trapping device (cold trap, filter, liquid trap) with a backflow check valve. 
2. Water, solvents, and corrosive gases are not allowed to be drawn into the building vacuum (house) system. 
3. When mechanical vacuum pumps are used with volatile substances, the input line to the pump is fitted with a cold trap to minimize the amount of volatile materials entering the pump and dissolving in the oil. 
4. If particulates could contaminate a vacuum line (e.g., from an inert atmosphere dry box or glovebox), a HEPA filter will be installed. 
5. If pump oil becomes contaminated, it is drained and changed to prevent the exhaust of chemicals into room air. 
6. Used pump oil is disposed of through ORS. 
7. Records of use are maintained for general-purpose lab pumps in order to forestall cross-contamination or reactive chemical incompatibility problems. 
8. The exhaust from evacuation of volatile, toxic, or corrosive materials is vented to an air exhaust system such as a chemical fume hood or local exhaust duct. 

Vessels 

1. Glass vessels used in conjunction with the vacuum system should be checked with polarized light for cracks, scratches, or etching each time the vessel is used. At minimum, a visual inspection will be conducted. 
2. Dewar flasks are wrapped with tape or enclosed in wooden or metal containers. 
3. Reduced pressure is never applied to flat-bottomed flasks unless they have been designed for this purpose. 
4. Vacuum desiccators are made of borosilicate/Pyrex glass or plastic. 
5. Evacuated dessicators are never carried or moved. 
6. Lab workers wait to open dessicators until atmospheric pressure has been restored. 
7. If rotary evaporators are used, increases in rotation speed and application of vacuum to the flask are gradual.