All standard shipping containers come with small circa 1 inch square vents on the top rails. This doesn’t allow for significant air flow but it does mean they are not airtight
You may also find on a used shipping container that the doors seals may not be in perfect condition, and also minor damage or war tot he floor over time may mean that there is capacity for a tiny bit of air flow through the floor (although this is unlikely). Door seals are only designed to prevent water from waves penetrating past the doors and damaging any cargo inside, they are not designed to be be airtight.
Refrigerated shipping containers however do not have the same vents, they come with metal floors and if the seals are fully intact they should be considered airtight for health and safety purposes (for example limiting time spent inside a closed space or monitoring systems to check on anyone working withing such an environment).
Wear and damage to any of the heat exchangers in the refrigerated container engine, mounting problems or other engine bay damage can mean that the refrigerated containers may not be perfectly airtight. Similar to above the door seals are not specifically designed to be perfectly airtight and on a used refrigerated shipping container some wear and partial damage to the seal may be evident.
Of course every shipping container we sell as standard is offers with our wind & watertight guarantee. This does not guarantee thew unit is airtight, not does it guarantee its watertight to the extremes of dropping the whole container into the sea and expecting it to float – we are simply guaranteeing that the container we offer for sale is good to keep your goods dry and out of the weather whilst used in a static, on site storage basis.
If your looking to source a shipping container please feel free to browse our online catalogue, we also have lots of helpful tips and guides in our news section, and you can of course contact us if you have any questions.