IMPLODING DEWAR

A researcher was about to prepare an ice trap in a Dewar to cool a stationary stainless steel receiver on a chemical reactor system. The researcher had positioned the Dewar on a laboratory jack stand and had raised the Dewar into position. The Dewar imploded, propelling glass shards toward the researcher, who fortunately was wearing prescription safety glasses and received only minor facial cuts. The researcher should have been wearing a full-length face shield and should have had a cover on the Dewar.

should be used whenever there is a possibility of breakage.

Styrofoam buckets with lids can be a safer form of short-term storage and conveyance of cryogenic liquids than glass vacuum Dewars. Although they do not insulate as well as Dewar flasks, they eliminate the danger of implosion.

6.E.3.3 Desiccators

If a glass vacuum desiccator is used, it should be made of Pyrex or similar glass, completely enclosed in a shield or wrapped with friction tape in a grid pattern that leaves the contents visible and at the same time guards against flying glass should the vessel implode. Plastic (e.g., polycarbonate) desiccators reduce the risk of implosion and may be preferable, but should also be shielded while evacuated. Solid desiccants are preferred. An evacuated desiccator should never be carried or moved. Care should be taken in opening the valve to avoid a shock wave into the desiccator.

6.E.3.4 Rotary Evaporators

Glass components of the rotary evaporator should be made of Pyrex or similar glass, completely enclosed in a shield to guard against flying glass should the components implode. Increase in rotation speed and application of vacuum to the flask whose solvent is to be evaporated should be gradual.

6.E.3.5 Assembly of Vacuum Apparatus

Vacuum apparatus should be assembled so as to avoid strain. Joints must be assembled so as to allow various sections of the apparatus to be moved if necessary without transmitting strain to the necks of the flasks. Heavy apparatus should be supported from below as well as by the neck. The assembler should avoid putting pressure on a vacuum line. Failure to keep the pressure below 1 atmosphere could lead to the stopcocks popping out at high velocity or to an explosion of the glass apparatus. Such increased pressure could result from warming of the contents of the trap due to failure to maintain low temperatures.

Vacuum apparatus should be placed well back onto the bench or into the hood where they will not be inadvertently hit. If the back of the vacuum setup faces the open laboratory, it should be protected with panels of suitably heavy transparent plastic to prevent injury to nearby workers from flying glass in case of explosion.

6.F USING PERSONAL PROTECTIVE, SAFETY, AND EMERGENCY EQUIPMENT

As outlined in previous chapters, it is essential for each laboratory worker to be proactive to ensure the laboratory is a safe working environment. This attitude begins with wearing appropriate apparel and using proper eye, face, hand, and foot protection when working with hazardous chemicals. It is the responsibility of the institution to provide appropriate safety and emergency equipment for laboratory workers and for emergency personnel. (See also section 5.C.)

6.F.1 Personal Protective Equipment and Apparel

6.F.1.1 Personal Clothing

Clothing that leaves large areas of skin exposed is inappropriate in laboratories where hazardous chemicals are in use. The worker's personal clothing should be fully covering. Appropriate laboratory coats should be worn, buttoned, with the sleeves rolled down. Laboratory coats should be fire-resistant. Those fabricated of polyester are not appropriate for glassblowing or work with flammable materials. Cotton coats are inexpensive and do not burn readily. Laboratory coats or laboratory aprons made of special materials are available for high-risk activities. Laboratory coats that have been used in the laboratory should be left there to minimize the possibility of spreading chemicals to public assembly, eating, or office areas, and they should be cleaned regularly. (For more information, see the OSHA Personal Protective Equipment Standard (29 CFR 1910.132) and the OSHA Laboratory Standard (29 CFR 1910.1450).)

Unrestrained long hair and loose clothing such as neckties, baggy pants, and coats are inappropriate in a laboratory where hazardous chemicals are in use. Such items can catch fire, be dipped in chemicals, and



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