ADT123:
You haven't stated WHAT killed the van's driver. If it was asphyxiation, you're onto something that points towards the CO2 level inside the van being excessive and maybe causing the driver's death. However, if the driver didn't suffer physical trauma or serious body wounds, then the CO2 issue becomes very "iffy" and debatable. Allow me to try to explain:
I have personal and extensive experience with continuous exposure to so-called "high" levels of CO2 and I can assure you from first-hand experience that the first thing(s) that a human being becomes aware of is the increasing level of asphyxia. It just doesn't happen from one second to the other. With CO2, it doesn't happen as it happens with CO (Carbon Monoxide). CO is toxic and poisons the victim by first rendering the subject unconsious. This is not what CO2 causes. A person exposed to continually increasing levels of CO2 in his breathing space will detect the effect as it starts and will identify a danger in proceeding to remain in the same confined environment - unless, of course, if he is unconsious from other effects (like a blow to the head) or constrained by a locked seat belt (both of which you haven't mentioned). Ammonia has a similar first effect on humans: it is detected almost immediately and with only a few ppms required. The immediate human reaction is a reflexive one: a mad rush to seek clean, fresh breathing air! Although the CO2 effect is similar to Ammonia's, it is much slower and not as accurate at the low concentrations - but nevertheless, it does yield a warning signal, albeit small.
I have stated this countless times before and I hate to repeat myself, but I'm afraid it's required again: CO2 is definitely NOT TOXIC! Carbon Monoxide, Ammonia, and Chlorine are definitely TOXIC - but not CO2. Any non-toxic gas like Nitrogen, Helium, or Argon will cause death by asphyxiation (much like CO2) if the victim is not allowed a fresh supply of breathing air. Properly designed ventilation is always one of the top priorities that one must design for and have available where human beings are involved. In fact, one of the key positive features of CO2 vapors generated by Dry Ice sublimation is the fact that, as 25362 has accurately pointed out, the -109 oF vapor causes a distinct and clearly visible WHITE FOG. This fog is nothing more than atmospheric water moisture that is condensed at the -109 oF temperature and is no more "toxic" than the CO2 vapor. This white mist is so ordinary that it is commonly used in "spooky" films, TV programs, Halloween apple bobings, Rock & Roll Concerts (in closed, un-monitored auditoriums!) and many other entertainment events. My point here is that it is a clear indication of the existance of cold CO2 in the immediate environment to a potential victim who should heed the warning. No such indication occurs in the case of N2, He, & Ar. As everyone on this forum must be aware, CO2 fire extinguishers are a "dime a dozen" and found literally everywhere. Yet, no special breathing apparatus or precautions are demanded of its use - other than common horse sense in furnishing proper ventilation. I would be so bold as to assert that a CO2 fire extinguisher was probably in the van! And does anyone question or suspect that? (The white fog seen in the discharge of a CO2 fire extinguisher is EXACTLY the same effect as the sublimation of Dry Ice.)
Sublimation rates depend on a variety of factors, as appropriately noted by some of the above respondents to this thread. Without accurate and definite information on the existing ventilation, temperature, van conditions, victim's awareness, etc, one cannot even make a credible estimate or approximation of the amount of CO2 that would have sublimed within the available time. The sublimation rate is a horse-sensical matter: the more available heat sink that is brought in contact with the Dry Ice, the faster the sublimation rate! Paradoxically, as the Dry Ice sublimes, it forms it's own very effective cap of insulation and protection: the sublimed CO2 vapor!! Unless mechanical or convection currects are induced or produced, the sublimation rate falls rather than increases!
Another item: was the victim upright? As 25362 again points out, the heavier CO2 will precipitate to the lowest region in the van (if the van is almost hermetically closed, without any outside ventilation - of which we know nothing) and give the victim more time to take action or make a decision. Again, I stress the fact that the victim will not black out; if constrained and forced to breath heavier doses of CO2, he would get progressively weaker and weaker - but he would be aware of it.
I heartily agree with IRstuff in that the real, positive proof that CO2 could have asphyxiated the victim is to simulate the accident with an identical van, Dry Ice shipment, conditions, etc. As far as generating any positive help on that determination via the use of sublimation equations (none exist, I can assure you), I believe that is too difficulat due to the scarcity of the basic data given on the incident.
Right at this moment there are perhaps hundreds of tractors pulling semitrailers loaded with tons upon tons of Dry Ice throughout our country on a daily basis. There is no ventilation used in the trailer and the driver uses a forklift to remove the many large crates of boxed and wrapped Dry Ice. The driver actually goes into the parked trailer and removes each crate, working his way to the rear-most section of the trailer - of course, the trailer is open at this time. My point is that on an empirical and experienced basis, there are many people (beside myself) who can easily testify as expert witnesses (I already have in the past) to the fact that working with, transporting, and handling Dry Ice is not a dangerous nor toxic operation per se. This does not discount the possiblility that in your case the victim was asphyxiated with CO2. However, wouldn't a coroner's report bear this out?
I hope I have not added confusion to the problem, but rather that I succeeded in clearing some items up. I have always believed in keeping the potential dangers of all gases clearly focused and always in our engineering safety awareness. No gas (or chemical) is so benign that it can be discarded as a potential danger - and CO2 is no exception. I wish you success in your investigation.
Art Montemayor
Spring, TX
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