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Working with Hot and Cold Sources

Working with Hot and Cold Sources



The application of extreme temperature techniques is an essential part in scientific research and industrial processes. Hence adequate safety training is a prerequisite to avoid injuries.

High temperatures are often required for chemical reactions or distillations. Open flames are frequently used for sterilization and modification of laboratory and medical equipment.

On the other hand, very low temperatures are often necessary to control highly exothermic reactions and for cooling of instruments such as a nuclear magnetic resonance spectrometer or a Schlenk line.

Hot plates and Bunsen burners are commonly used for high temperature operations, while dry ice or liquid nitrogen is applied for extreme cooling. However, all of these sources can provide significant hazards if not handled carefully.

This video will illustrate the hazardous nature of extreme temperature techniques, how to safely operate and work with these sources, and what to do in case of an emergency.

A Bunsen burner uses methane, propane, or butane to create an open flame. The temperature of this flame can be roughly adjusted between 250-1200 degrees Celsius.

In comparison, a hot plate consists of a flat surface made of aluminum or ceramics and uses electricity to generate heat. Hot plates do not have open flames and can be controlled more accurately with temperatures ranging between 50-350°C.

If necessary, higher temperatures can be achieved with special hot plates reaching up to 1250°C. To avoid fire hazards, the open flames and high temperatures of hot sources should be handled very carefully.

Cold sources can be hazardous as well. Dry ice, which is the solid form of carbon dioxide, provides temperatures as low as -78°C. In addition to cold burns, excessive sublimation of dry ice could lead to carbon dioxide gas build up in a very short time, posing a danger of hypercapnia.

Lastly, liquid nitrogen - a cryogenic fluid - is used when even lower temperatures are necessary. It can provide a bath temperature as low as -196°C.

Liquid nitrogen can expand 695 times in volume, and upon vaporization can cause extreme oxygen deficiency in the surrounding air, leading to suffocation, unconsciousness, and death under extreme circumstances.

In addition, prolonged exposure to skin can quickly result in frostbite. Short exposure to the eye fluids can permanently damage the eyes.

Now that you know about the properties and hazards of the heat and cold sources, let's take a look at how to safely work with these components.

Before using any hot source, make yourself familiar about the location of a fire extinguisher and a fire blanket. Remove jewelry and tie back long hair. Always wear a lab coat, safety glasses, close-toed shoes, and gloves. You should also consider using thermal protective gloves, which insulate effectively up to 650 °C.

Clean the area of any combustible substances such as paper or chemicals. Place the Bunsen burner away from overhead equipment, or light fixtures by at least 12 inches. Check the hose connection to the gas source for any leaks and use appropriate signage to notify that burner is in operation. Use a lighter with an extended nozzle for lighting the burner.

Once the Bunsen burner is operating, never leave the open flame unattended. When you are done, close the valve on the Bunsen burner, shut off the gas immediately and close the connection to the gas source, letting the burner cool before handling or cleaning after use.

Many hot plates come with a built-in magnetic stirrer, digital read-out and a thermocouple input for adjusting and maintaining the temperature.

Like for the Bunsen burner, know the location of the fire extinguisher and which type to use. Never use water or liquid nitrogen to extinguish oil bath fire, but instead a class B fire extinguisher.

Always wear personal protective equipment while working with a hotplate. When heating volatile and hazardous substances, remove flammable or combustible materials from around the hot plate and place the hot plate in the hood.

Once you have familiarized yourself with the properties and scale of your experiment, choose the right size hot plate, heat resistant and crack free glassware made of borosilicate, and an oil bath.

Make sure the experiment temperature is below the flashpoint of your oil bath. Always use a condenser, when heating volatile solvents or substances.

If solvent needs to be added to the heated experiment, use a pressure-equalizing dropping funnel. Do not add solvent directly, as it might cause a flash fire. As with the Bunsen burner, do not leave the hot plate unattended.

Materials with a very low boiling point, such as diethyl ether, should be heated using a water bath instead of an oil bath to avoid a significant risk of fire.

If metal foil or metal containers, such as aluminum blocks, are used for heating, special attention and caution should be applied. In comparison to an oil bath, it is not possible to see if it is hot or cold, therefore always check the temperature with a thermometer and use heat-resistant gloves.

Now that you have learned about the use of hot sources, let's take a look at the other extreme - the cold sources.

Dry ice should be stored in a polystyrene container and if possible in a cold room to minimize sublimation. Store dry ice in properly ventilated areas to avoid hypercapnia. Do not use a completely airtight container to avoid expansion of the container and possibly an explosion caused by subliming dry ice.

Wear protective personal equipment when handling dry ice. For extra protection, you can wear cryogenic gloves, which contain a multi-layer insulation against the low temperatures. Furthermore, to obtain and transport small quantities of dry ice, use a big plastic scoop and a polystyrene bucket.

When finished, either put the clean dry ice back into the storing container or allow it to sublime. If a cooling bath was made using dry ice, dispose of it in the hazardous waste container. Never, dispose dry ice directly in the sink or trash can.

Liquid nitrogen is stored and handled using Dewars, which is a type of double-walled containers with a vacuum in between the walls.

Always wear protective personal equipment when handling liquid nitrogen. This includes insulating gloves and a facial mask, especially when pouring liquid nitrogen as the liquid tends to splatter.

Make sure all areas are well ventilated. When transferring liquid nitrogen, never fill the Dewar more than 80% full and never close the container tightly to prevent pressure build up. Furthermore, extra precaution should be taken when using a Schlenk line. If the cold trap is immersed in liquid nitrogen, and air is being pulled, it can condense oxygen into the cooling trap, creating explosive mixtures of liquid oxygen with organic materials in the trap.

Remember, that hot and cold sources can be a hazard and a health risk.

In case of a small fire use the appropriate extinguisher. If the fire is too large, pull the fire alarm or call 911. Evacuate the building following the emergency instructions of your institution.

In case of a skin burn caused by a hot source, hold the affected area under cold water for at least 10 minutes. In case of a cold burn, hold the affected area under tepid and not hot water for at least 10 minutes. Do not rub the affected area, apply a sterile dressing, and seek further medical attention.

In case of splashes of either very hot or cold substances in your eyes, immediately flush with copious amount of water using eyewash and seek medical attention.

In case of dizziness or consciousness loss, when working with liquid nitrogen or dry ice, move the affected person into a well-ventilated area and seek further medical attention if necessary.

You've just watched JoVE's introduction to working with hot and cold sources. You should now understand the hazards of these materials, how to safely work with them, and what to do in case of an emergency such as a fire or burn. As always, thanks for watching!

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