Quote:What emerges when food science and technology
are applied with a modern flourish to fine cuisine?
Answer: An edible menu made from
soybean paper and potato starch printed with fruit juice
ink; faux caviar made with sodium alginate and avocado
puree; aerated foie gras accompanied by pickled beet
and Mashhad plum; and culinary foams infused with
lemon, lime, or amaretto. These are but a few of the
in-demand food novelties created by chefs harnessing
scientific principles and applying them to food.

Quote:Nils and I wrote an article on freezing for the September 2009 issue of Food Arts Magazine. The piece included a short section on liquid nitrogen (LN or LN2), and I have greatly expanded it here for the blog. Important: we make no claims to inventing any of the techniques presented here. They are all pretty standard.

Nitrogen makes up most of air we breathe. It is completely and utterly non-toxic – end of story. Yes, it is a chemical. Cows and carrots are just collections of chemicals.
The dangers of Liquid Nitrogen, of which you must be ever vigilant, are cold-burns, asphyxiation, and pressure-related explosions.

Dangers to your customers:
Don’t serve items to your customers too cold. You will burn their tongue, spoil their meal, and make them angry. I am speaking from first hand experience here (as the burnee, not the burner).

Dangers to you, your co-workers, and your building:

Cold Burns:

Some do’s and don’ts. Do wear goggles or a face shield. Do Not wear clothes that could trap liquid nitrogen –like canvas shoes. Do Not use unprotected hands to hold on to things –like this bain—that might get instantly super-chilled. I got badly burned shooting this picture and couldn’t feel my fingertips for two days.

If a small amount of liquid nitrogen touches your skin and rolls off, you will not be harmed. Lab technicians routinely dip their bare hands directly into liquid nitrogen (quickly! they don’t hold their hands in it). A layer of vapor instantly forms and temporarily protects your skin—this phenomenon is called the Leidenfrost effect. Read a cool paper on the Leidenfrost effect, written by a science teacher who dips his hand in molten lead, here.

Burn danger occurs when liquid nitrogen remains in contact with your skin – whereupon liquid nitrogen burns the same way hot oil does. Painfully.

• Do Not wear clothing that can capture liquid nitrogen run-offs or spills, such as cuffed pants. I got my worst LN burn when my protective sleeve (which was not rated for cryogenic work – wrong choice) got too cold, cracked and allowed LN to seep into the cloth cuff of my gloves.
• Do Not dispense LN into a container, such as a bain marie, that you are holding with your bare hands. You will get burned if the container gets super-chilled, which is likely. This hurts, too.
• Always wear safety goggles – LN can boil up and into your face at any moment, quickly blinding you. Forever.
• Never pour LN above your head, and do not kneel next to someone pouring LN.
• Do Not hold containers of LN with one hand, or in any other precarious way.
• Have a clear exit path in case something goes wrong – if you drop a whole container of LN, you and everyone else around you needs to get away from it quickly.

Explosion:

Never seal liquid nitrogen in a closed container. The pressure will rise, and unless the container can hold 1000 psi or better (nothing you have can) it will explode. In July 2009 a young cook in Germany lost both his hands and landed in a coma when he sealed LN in a closed container. Liquid nitrogen containers, called dewars, are either completely vented to the atmosphere or held between 10 and 22 psi with multiple safety valves. It’s worth repeating: don’t put LN in a container that is sealed or could become sealed by mistake.
• Let’s put that last part another way: Make sure there is no way your containers could become sealed. Example: a venting tube in a lid could get clogged, or crimped. A thermos lid you leave unscrewed can be sealed by your colleague. Note that even if an explosion isn’t strong enough to cause damage, LN spraying all over the place is hazardous.
• Never send LN through a pipe that could become sealed. You’ll make a pipe bomb.
• Never modify a dewar. In 2006 at Texas A&M, someone intentionally defeated the safety valves on a LN storage dewar. The resulting explosion destroyed several rooms, tore a hole in the ceiling, and ruptured plumbing that in turn flooded the entire building. Thankfully all this happened at 3am, and no one was hurt. The pdf report complete with pictures is: here.

Asphyxiation:

Disposable Oxygen Meter. Runs for 2 years with no maintenance --then you get a new one. 180 bucks. McMaster Carr part number: 18995T51.

A small amount of liquid nitrogen turns into a large amount of nitrogen gas –LN expands by 700 times when it vaporizes. If you use a lot of LN in a closed space, it will displace the oxygen and suffocate you before you know what’s happening. This is the largest cause of death from LN. The danger is very, very real.
Unless you have been trained like an air force pilot – by coming up to the very brink of nitrogen-induced death under highly controlled circumstances – you can’t tell that you are suffocating on nitrogen. The panicky feeling you get from choking or staying under the water too long doesn’t come from lack of oxygen — it comes from the buildup of CO2 in your blood. Your lungs can get rid of CO2 just fine in a pure nitrogen environment, so your body doesn’t send those helpful distress signals. Also, breathing pure nitrogen is much worse than just holding your breath. Breathing nitrogen actually sucks the existing oxygen out of your bloodstream. Majorly bad news. So,
• Do Not use LN in an unventilated area. What constitutes an unventilated area? Read ASU’s guidelines here.
• Never go into an elevator with LN. If a dewar breaks in the elevator, you’re dead.
• Never carry LN in a vehicle’s passenger compartment. You get into an accident, the LN spills and vaporizes, you suffocate instantly.
• If you see someone passed out near an LN tank, do not try to help. Many people who die from nitrogen suffocation were trying to help co-workers. If the victim has passed out they are probably already dead. Call 911.
• Invest in an oxygen meter, like the one shown in the picture above.
• We can’t cover every eventuality here – be sensible.

Set up and enforce a safety program:
Make sure everyone who uses LN is properly trained. Print out and post basic LN Safety rules. Some documents:
An overview of the hazards (plus gruesome details) from the US Chemical Safety Board.
The cryogenic fluids handling guide from Arizona State University.