transportation of dry ice on aircraft 1

[PhilLee]

I am working with the Dangerous Goods Coordinator of our small airline with the issue of dry ice. There are very broad guidlines which the aviation industry uses regarding amounts of dry ice that can be safely, however we have concerns that these values may be too high for the smaller volume of our cargo holds. We have had one incident where a package with a small amount of dry ice stored in a fairly large walk-in freezer caused an employee to pass out. Fortunately he was not working alone. We don't want something similar to occur in the air...

I need to calculate the amount of CO2 gas produced by a box of dry ice measuring 12"x12"x12".

variables
Pressure: 7,000 ft altitude (cabin pressure)
Temperature: 15deg celcius (cabin temp)
Time: 3hrs
Insulation: 0 (packed in fibre board box)

Let me know if there is additional info required...
Thanks,

 

[quark]

Generally, dry ice sublimes at a rate of 8-10 pounds(4536 gms) in 24 hours.

One mole (or 44gms of dryice) of dry ice produces 22.4 liters of CO₂ gas. So CO₂ gas produced in 3 hours would be

(4536 x 22.4 x 3)/(44 x 24) = 289 liters or 0.289M³

5%v/v concentration of CO₂ is fatal.

Infact, the rate of sublimation will be high as you are creating more air flow across the dry ice by the walk in freezer fan.

Some suggestions.

1. Why can't you check actual rate of sublimation by weighing the dry ice after 3 hours?
2. CO₂ monitoring system inside the freezer will help you.
3. Try to store it in an insulated box.
4. Either provide fresh air into the freezer to negate CO₂ concentration or provide breathing suits to employees (this will be a cheaper option).

Regards,


Believe it or not : Had we trusted Archimedes and assigned him the work of lifting the earth(or any mass equivalent to that of earth on earth),with a lever of suitable length, it would have taken him 23 million million years to lift the earth by one centimeter.

 

[25362]

A 12"x12"12" block of dry ice would have a mass of about 44 kg or 1,000 mols or about 22.4 cubic meters at STP conditions. At 0.77 atm and 15 deg C the volume estimated by quark would be 0.289 * [(15+273)/273] *1/0.77 = 0.4 m³.

At about 5% in air carbon dioxide causes a threefold increase in breathing rate. Prolonged exposure to concentrations higher then 5% may cause unconsciousness and death.

Ventilation to prevent accumulation of dangerous CO₂ % must be provided. Absorption of gaseous CO₂ could be attained by scrubbing the gas through solutions of alkali carbonates.

Be careful !

 

[PhilLee]

quark,
Can you provide the formula for calculating the 4,536grams per 24 hrs. I presume that it is assuming sea level and some ambient temperature? Not that I don't trust it, i just like to see how the values are derived!!!

25362,
Can you provide the units for the pressure / temperature correction calculation?

thanks to both of you!

 

[25362]

The ideal gas law PV=RT is the basis for conversion. Thus (PV/T)_actual=(PV/T)_STP.

Since STP conditions are P=1 atm absolute, T=0^oC=273 K, V=0.289m³, and the actual conditions are a cabine pressure equivalent to an altitude of 7000 ft representing (if I'm not mistaken) a pressure 77% of the atmospheric pressure at sea level, and T=15^oC= (273+15) K, the corrected volume would be

V_actual=(PV/T)_STP*(T/P)_actual= (1*0.289/273)*[(273+15)/0.77]=0.4 m³

 

[quark]

PhilLee!

You are most welcome even if you don't trust, for this site or the members who reply don't hold a liability

and it is always better to check the things once again. The sublimation rate I stated above was indeed at sea level and ambient temperature(it is practically figured out quantity). As the cabin pressure is maintained irrespective of altitude, I didn't take any correction for the rate of sublimation.

Upon searching yahoo with the keywords 'sublimation of dry ice with altitude' I came across this link which suggests that the concentration of CO₂ should not be more than 3%. Even if I consider a sublimation rate of 10lb/24hrs, your freezer volume should be not less than
(0.289 x 100)/3 = 9.6M³If the cabin pressure is not maintained, you should follow 25362's correction for the volume.

http://www1.faa.gov/avr/arm/co2rule.doc

I do let you know, if I come up with any useful information.

Regards,


Believe it or not : Had we trusted Archimedes and assigned him the work of lifting the earth(or any mass equivalent to that of earth on earth),with a lever of suitable length, it would have taken him 23 million million years to lift the earth by one centimeter, if he worked at the rate of 1 HP.

 

[PhilLee]

Thanks quark,

The cabin pressure is indeed maintained relatively constant once the aircraft reaches cruising altitude. However it is not maintained at sea level, it is at approx 6,500 to 7,000 ft producing a pressure differential of about 6 psi. Otherwise the pressure differential would be huge and the airplane would have to be designed so heavy it wouldn't fly! (Not really, but you get the drift!)

By assuming this pressure for the entire flight, we have a conservative answer, as the pressure is in fact higher during ascent and descent.

Thanks for the FAA link...I hadn't found that one yet.

Phil

 

[JOM]

Hi PhilLee,

In our original post you said:

"We have had one incident where a package with a small amount of dry ice stored in a fairly large walk-in freezer caused an employee to pass out. Fortunately he was not working alone. We don't want something similar to occur in the air..."

"Fortunately" he was not working alone? Well, since it turned out OK, I suppose that's true.

A very common scenario is this: Employee 1 collapses, employee 2 goes to help, Employee 2 collapses...firemen remove two bodies. It happens soooo often. Sometimes three or four bodies.

Since carbon dioxide is deadly, why carry it? Would you carry a cardboard box of rattlesnakes?

Hope you find a safe answer.

;-)


Cheers,
John.

 

[aviat]

PhilLee
As you know the transportation of dangerous goods by air is covered by IATA Dangerous Goods Regulations; a copy of regulation is available at:

http://www.iataonline.com/store/default

It lists the amount of carbon dioxide that you can carry (in this case .5 kg per person max with a max of .5 kg per pkge) and the labels and hazard (spontaneously combustible).
As mentioned above the mass is 44 kg; this would have to be packaged in seperate inner and outer packages.

Most people have gone away from dry ice because of the extra expense of dangerous goods. If the fish etc. is already frozen, you can wrap it in a plastic bag and then ship in a box insulated with styrofoam. It will stay frozen for the length of flight.

I was once looking at the faa site and there were well known companies getting fines for a million dollars for not declaring dangerous goods.

Cheers

 

[Montemayor]

For many years I produced mega-tons of Dry Ice specifically for use as a refrigerant medium on pre-cooked meals and other consumables on commercial passenger aircraft in the USA and also on international flights. Regardless of what some un-informed persons (like JOM) may think, this was (and still is) very safe. CO2 is only dangerous when it displaces the necessary Oxygen that we breathe. It is also dangerous when generated by a quantity of Dry Ice that is contained and sealed in a container that has no relief method available to it. But these ordinary and commonly known characteristics of CO2 and Dry Ice should be well-known and designed-for by engineers.

Believe me folks, there is no cause for alarm. Dry Ice has been used as a commercial, direct contact refrigerant since the 1920's when it was introduced for street vendors hawking ice cream - and it still fulfills that application world-wide. Quark's empirical figure is approximately correct for many applications - depending on local and specifics on the application. 25362's recommendations on proper and normal ventilation always being furnished are precisely on target. This is what should be done on all Dry Ice applications - because of the obvious sublimation gaseous product. To date, I know of no other refrigeration method that can compete economically and practically with Dry Ice in air planes. However, a knowledgeable and horse-sense design must be adhered-to - like providing adequate ventilation and keeping your hands off the -109 oF solid Dry Ice!

Art Montemayor
Spring, TX

 

[JOM]

Hi Art,

You said:

"Regardless of what some un-informed persons (like JOM) may think"

Your remark disappoints me, Art.



Cheers,
John.

 

[Montemayor]

JOM:

I regret if my remark regarding the relative safety and dangers of Dry Ice application may have disappointed you. I also can asssure you that no insult, put-down, or demeaning was meant by my use of the term "un-informed". Rather, what I have always expressed to users and consumers of Dry Ice is the fact that it is not dangerous if used in an informed and experienced manner.

Now that I have expressed what I know as personal and first-hand experience in producing and handling Dry Ice for many years, I hope that you can see the contrast with your statement stating that "carbon dioxide is deadly" and akin to "a cardboard box of rattlesnakes". This is just not true, in my opinion. If true, water would also have to be labeled as deadly because people drown in it. Additionally, it would then be criminal of the air transport industry to employ it. However, the opposite is true. Both Carbon Dioxide and Dry Ice are being handled everyday in commercial applications world-wide in some rather backward and under-developed countries under routine conditions and without need for worry about tragic accidental deaths. People who work with it take the appropriate steps in handling the substance. That's what makes it possible to have a cold Pepsi or Coca-Cola in many underdeveloped parts of the world today.

Again, while I cannot apologize for stating what I believe is fact, I want to make sure that people on this forum understand that carbon dioxide is not like carbon monoxide. It is not toxic nor a poison. Like any other gas (other than Oxygen), it will cause asphyxiation or death if it displaces Oxygen. But this is true of all other gases also! I hope you do not take my remark as trying to demean or insult your opinion or comments; I always try to use this forum as a means to share factual engineering experience and knowledge and not to promote personal feelings or opinions.

Art Montemayor
Spring, TX

 

[PhilLee]

I agree with Art in that dry ice is a reality, and if safely handled poses no threat to human health. We operate where there are no other options, and we don't have the choice to simply not carry it.
We are actually implementing internal guideliens that are more restrictive than the IATA guidelines...
Thanks for the good discussion guys...

 

[JOM]

Hi Art.

I appreciate the thoughtful reply. I know you're not one to put down or attack another forum contributor.

One thing you're right about - I am "uninformed" regarding air cargo operations. Know nothing about it at all. Don't know too much about CO2 production and use either. But I know something about the hazards of inert gases and confined space fatalities.

I monitor industrial accidents and one of the most distressing aspects is the continuing repetition of confined spaces fatalities. They go on, and on, and on, and on....

Phil was after assistance with a challenge he can't avoid and telling him not to carry the stuff was no help. But then again, stressing the need take caution doesn't hurt, does it?

Am I really mistaken to describe CO2 as "deadly"? I know of a case where a bar worker died from CO2 that was leaking into the beer keg cellar from the bottles used to pressurise the kegs. There is another case of a lab scientist dying in small room where biological specimens were preserved in liquid nitrogen. The room filled with gaseous nitrogen and asphyxiated him. Phil tells us that they have had a cargo handler collapse.

The victims are often, perhaps mostly, people who do not understand the danger. I think most people know you can drown in water, but I would say most people do not know you can die from CO2.

Getting off-topic.
;-)

Cheers,
John.

 

[PhilLee]

John,
I appreciate your perspective, you're correct, we have no other option and this whole excercise is to become more informed and thereby avoid a diaster.

While there are guidelines out there published by IATA, it is our concern that there is insufficient specifics for smaller aircraft. Especially of concern are shipments that are transferred from larger aircraft to smaller aircraft.
Furthermore, blindly following these guidelines has not and will not stand up in court, each operator must ensure that their handling procedures are safe. Hence my questions....!

Further to my question to Quark regarding a formula for the sublimation rate. He refers to a 'practically figured out' figure of 10lbs/24hrs at sea level and ambient temperature (what ambient temperature? 0C? 15C? Our cabin ambient temp is 15C). Surely this rate can be calculated?!?! Is it not a simple heat loss calculation? It seems logical to me but I still can't find the formula...

Any comments??

Best regards,
Phil

 

[Compositepro]

I too am unsure that you can have a rule of thumb on sublimation rate. It is, indeed, a heat tranfer with many uncontrolled factors. One of the most important factors I have found is whether the box is tightly sealed on the bottom. The cold CO2 gas is much heavier than air so if the seams of the box are not tightly sealed the CO2 will just pour out the bottom and be replaced with warm air coming in at the top (thermosiphoning). This increases the CO2 sublimation rate many fold. This also results in wet boxes because the water frost will accumulate in the box. The CO2, of course must be allowed to vent.

I would suggest that safety could be improved if dry iced packages were placed in open top tubs that were connected to exhaust ventilation. Exhaust ventilation is required in any confined space that will contain people and CO2. This approach would simply reduce the exhaust flow rate requirement to the absolute minimum.

 

[PhilLee]

The dry ice is packaged per IATA Dangerous Goods guidelines which require it to be carried in a std cardboard box with 1 strip of tape accross both the top and bottom seams. This allows for venting through the side seams on both the top and bottom.

FYI
The exchange of the cabin air is another variable that I am accounting for once I have calculated the amount of CO2 produced.

 

[25362]

PhilLee, it would be difficult to estimate the rate of sublimation in a confined space without air moving around and only by radiation when the dry ice block is surrounded by cold gas and moist air.

Anyway, the figure of 10 lbs over 24 hours is indeed a ROT rate given for a typical thermally insulated ice box, it can be higher or lower depending on the packaging conditions of the dry ice, its contact with warmer items, the exposed surface, etc.

If the ambient pressure of the cabin is lower than atmospheric, say 0.8 atm abs, the sublimation is quicker and the temperature is even lower than the conventional -78.5^oC by about 10 degrees Celsius.

It has been said that CO₂ is about 1.5 heavier than air; a colder gas would be even much heavier and tend to accumulate at low and confined spots where its concentration may become sufficiently high. Appropriate ventilation and air mixing are sine qua non conditions, and, of course, nobody should bring his/her face near these low "sump" areas to avoid breathing the hazardous "atmosphere".

Another point that comes to mind, is the risk of freeze burns on exposed skin. Although a brief contact is considered harmless, dry ice should be handled with care using suitable gloves. Total body covering and face shielding when breaking up blocks of dry ice are usual personal protective procedures known to those who handle it on a regular basis. Good luck.

 

[JOM]

Phil,

Why did the cargo handler collapse in a large space containing a small amount of CO2? What went wrong? Can it happen again?

Can I ask if it is possible for CO2 to travel from its storage location to the pilot(s)?

Cheers,
John.

 

[25362]

I pressume dry ice stored in the luggage compartment of an air carrier, where pressures are sometimes lower, may sublimate much quicker.