Dry ice is one of the safest cold sources a lab can keep on hand, right up until it is stored in the wrong place. It does not burn. It does not explode under normal handling. It is not toxic. The entire hazard profile comes down to one quiet fact: it sublimates continuously into carbon dioxide gas, and CO₂ displaces the oxygen in enclosed spaces.
The problem is that the enclosed spaces where CO₂ accumulates are exactly the places labs tend to store dry ice: walk-in cold rooms, small windowless storage closets, the back of a delivery van, a chest freezer in a corner. The gas is invisible, it has no strong odor, and by the time a person feels it, judgment is already impaired. Every serious dry ice incident in a lab traces back to CO₂ in a confined space, so that is where safety planning starts.
The one number that anchors everything: 5,000 ppm
Normal outdoor air is about 400 ppm CO₂. The number that matters for the lab is the OSHA permissible exposure limit of 5,000 ppm (0.5% by volume), averaged over an 8-hour workday. That is the broadly accepted line for how much CO₂ a person can breathe all day without harm.
Above it, effects begin and escalate:
Around 5,000 ppm: the 8-hour exposure ceiling. Prolonged exposure above this starts to matter.
Around 30,000 ppm (3%): headache, elevated breathing and heart rate, noticeable discomfort. This is also a common short-term exposure limit reference for a 15-minute window.
Around 40,000 ppm (4%): immediately dangerous to life and health. Judgment and coordination degrade fast.
Higher still: loss of consciousness, and the person cannot self-rescue.
The reason CO₂ is dangerous rather than merely uncomfortable is that it displaces oxygen and dulls the very judgment a person would need to recognize the problem and leave. This is not a gas that gives clear warning.
How much CO₂ a subliming block actually produces
The math is worth doing once, because it makes the risk concrete. Dry ice sublimates at roughly 1 to 2% of its mass per day in typical storage, faster in warmer or less insulated conditions. One pound of dry ice, fully sublimated, produces about 8.3 cubic feet of CO₂ gas.
So a 50 lb delivery sitting in storage is slowly releasing hundreds of cubic feet of CO₂ as it sublimates. In a large, ventilated room that gas dissipates and the concentration never climbs. In a small closed storage closet, a walk-in freezer, or a stalled delivery vehicle, it accumulates, and it accumulates low, because CO₂ is denser than air and pools near the floor. That is the whole risk in one sentence: a safe amount of dry ice in a well-ventilated room becomes a hazard the moment the same amount sits in a sealed small space.
The three spaces that cause incidents
Walk-in cold rooms and freezers. A person enters, the door seals behind them, and dry ice inside has been building CO₂ with no air exchange. Cold rooms are the classic scenario because they are both enclosed and a natural place to put dry ice. Never store significant dry ice in a walk-in without confirmed ventilation or CO₂ monitoring, and never let someone work alone in one that holds dry ice.
Small storage rooms and closets. A windowless supply closet with dry ice in it is a slow CO₂ accumulator. Storage should be in a well-ventilated area, ideally not a sealed room, and never in a basement space with poor air exchange.
Vehicles. Transporting dry ice in a closed passenger cabin is a documented cause of incidents. If dry ice rides in a vehicle, it belongs in a ventilated cargo area, with windows cracked, and never in a sealed trunk with occupants nearby. This applies to the quick run across campus as much as the delivery route.
The other hazard: cold burns
The second, milder risk is direct contact. Dry ice sits at −78.5 °C. Skin contact for more than a moment causes frostbite, effectively a burn from the cold side. This is straightforward to prevent:
Handle dry ice with insulated cryogenic gloves, not thin nitrile or bare hands. Ordinary lab gloves are not enough for sustained contact.
Use tongs or a scoop for handling loose pellets.
Wear eye protection when breaking or cutting blocks and slabs, since fragments can fly.
Never put dry ice in your mouth, and never let it contact skin directly for more than an instant.
Storage: containers that vent, spaces that breathe
The storage rule is the mirror image of the air-shipping rule, and it exists for the same reason. Never store dry ice in a sealed, airtight container. As it sublimates, the CO₂ builds pressure, and a truly sealed container can rupture. Store dry ice in an insulated container designed to vent, an insulated cooler with a loose lid or a dedicated insulated tote, in a ventilated space.
Do not store dry ice in a standard −20 °C or −80 °C freezer as a matter of course. The freezer's thermostat will sense the extreme cold, shut off the compressor, and the built-up CO₂ has nowhere to go. Dry ice storage belongs in insulated containers at room ambient, in an area with air exchange, used on a short cycle so it does not sit long enough to become a large CO₂ source.
When a lab should have a CO₂ monitor
For most labs handling modest quantities in well-ventilated spaces, careful storage and handling practice is sufficient. A fixed or portable CO₂ monitor with an audible alarm becomes appropriate when any of these are true: dry ice is stored or used in a walk-in cold room, quantities are large and stored in a confined space, the storage area has limited ventilation, or personnel routinely enter a space where dry ice accumulates. The alarm should be set to alert well before the 5,000 ppm workday limit, giving people time to ventilate or leave. Personal CO₂ badges are also available for staff who work regularly around dry ice in tight spaces.
A short lab checklist
Store dry ice in a vented insulated container, never airtight, in a ventilated area.
Keep it out of sealed small rooms, sealed walk-ins without monitoring, and closed vehicle cabins.
Handle with cryo gloves; use eye protection when breaking blocks.
Put a CO₂ monitor in any enclosed space where dry ice is stored or accumulates.
Do not let anyone work alone in a cold room that contains dry ice.
Order on a short cycle so quantities do not sit and build up as a CO₂ source.
Questions we get asked
Is dry ice dangerous to keep in the lab overnight? In a vented container in a ventilated room, a normal working quantity is low risk. The danger comes from sealing it in a small unventilated space. Storage location matters more than storage duration.
What CO₂ level should a monitor alarm at? Set the first alarm below the 5,000 ppm 8-hour limit so people are warned early. Many facilities set a low alarm around that level and a high alarm well below the 30,000 ppm short-term range.
Can I store dry ice in a −80 °C freezer? It is generally discouraged. The freezer reads the extreme cold and shuts off its compressor, and the sealed cabinet traps CO₂. Use vented insulated containers instead.
How fast does dry ice disappear in storage? Roughly 1 to 2% of mass per day in a good insulated container, faster in warm or poorly insulated conditions. Order quantities matched to use so it does not linger.
The summary, on one line
Dry ice is safe in a vented container in a ventilated room and dangerous in a sealed small space, because it sublimates into CO₂ that displaces oxygen; keep it out of closed rooms and vehicles, monitor enclosed storage against the 5,000 ppm limit, and handle it with cryo gloves.
Cryo Life Solutions supplies pelletized and slab dry ice to research labs, universities, and biotech facilities across the Northeast US, on delivery schedules sized to match use so quantities do not sit and accumulate. Standing orders available across MA, NH, RI, CT, NY, NJ, and PA. Call 603-802-6650 or email info@cryolifesolutions.com.
Related reading: Dry Ice for Biotech and Pharma Cold Chain: A Working Guide for Northeast US Operators
