How an ice-lined refrigerator works
An ILR is a top-opening refrigerator with a lining of sealed water containers — ice packs or tubes — fixed around the inside walls. While power is on, the compressor freezes that lining; when power fails, the frozen lining keeps absorbing heat and holds the cabinet in the +2 to +8 °C band. The handbook describes ILRs keeping vaccines safe with a minimum of 8 hours' continuous electricity in a 24-hour period.
The top-opening design matters as much as the lining. Cold air is denser than warm air, so it stays in a chest when the lid lifts, instead of spilling out as it does from an upright door.
How the programme uses deep freezers
The programme's deep freezers are also top-opening, but they hold −15 to −25 °C. At district level and above they store OPV and rotavirus vaccine; at sub-district cold chain points they are supplied for freezing ice packs, while all routine vaccines are kept in the ILR.
A deep freezer has no ice lining, so its hold-over during a power cut depends heavily on how many frozen ice packs are inside and how often the lid is opened. The handbook advises that a freezer storing vaccines should not also be used to freeze fresh ice packs, because loading warm packs raises the cabinet temperature.
Hold-over time: the number that matters in an outage
Hold-over time is how long the equipment takes, after a power cut, to warm from its operating temperature to the top of its safe range. For an ILR that means reaching +8 °C.
- Higher room temperature shortens hold-over — a 43 °C store room costs hours.
- Every lid opening lets cold out; use the basket and plan picks.
- A full, well-spaced load holds cold better than a nearly empty cabinet, but crowding blocks air.
- A fully frozen lining gives the full hold-over; a partly melted one does not.
Loading an ILR: top and bottom are not the same
Inside an ILR the bottom is colder than the top, because cold air sinks. The handbook therefore divides the cabinet into zones: freeze-sensitive vaccines such as DPT, TT, Hepatitis B, IPV and Pentavalent go in the upper part of the basket, while vaccines that tolerate cold better — OPV, BCG, measles, rotavirus and JE in the handbook's list — can sit lower down.
All vaccines go in the basket supplied with the ILR, never on the cabinet floor. If the basket is missing, the handbook suggests laying two layers of empty ice packs flat on the floor as a barrier. Leave space between boxes, place a thermometer among the vaccines, and arrange stock so the earliest expiry is used first.
Stabilisers and power
The handbook is firm that electrical cold chain equipment should never run without a voltage stabiliser, and that one stabiliser should not be shared between machines. It describes normal stabilisers for roughly 150–280 V input and low-range versions down to 110 V or 90 V for areas with very weak supply, and warns against bypassing a faulty stabiliser.
For anyone running pharma or vaccine storage outside the programme, the same logic applies: know your site's real voltage range, choose protection that covers it and fix protection faults as urgently as the fridge itself.
Twice-daily checks and eVIN
ILR and deep freezer temperatures are recorded twice a day, every day, in a log kept with the equipment. On top of that manual record, the electronic Vaccine Intelligence Network (eVIN) — introduced in 2015 under the National Health Mission — adds SIM-enabled temperature loggers that record cabinet temperature and send SMS and email alerts to cold chain technicians and managers when a reading goes out of range. The same system tracks vaccine stock through a smartphone app.
ILR and DF compared
| Ice-lined refrigerator | Deep freezer | |
|---|---|---|
| Cabinet range | +2 to +8 °C | −15 to −25 °C |
| Typical contents | All routine vaccines at sub-district points; most vaccines elsewhere | OPV and rotavirus at district and above; ice packs |
| Outage protection | Frozen water-pack lining | Only frozen packs kept inside |
| Opening | Top lid | Top lid |
| Key handling rule | Basket only; freeze-sensitive vaccines at the top | Don't freeze new ice packs in a vaccine-storing DF |
Frequently asked questions
- Why must vaccines never sit on the floor of an ILR?
- The floor is the coldest part of the cabinet and can drop low enough to freeze freeze-sensitive vaccines. Programme guidance keeps all vaccines in the basket, with freeze-sensitive ones in the upper part.
- Can a private clinic buy an ILR?
- Ice-lined designs are sold commercially, and they make sense where power cuts are long. A private clinic still follows product labels and its State Drugs Control authority; the programme's handbook describes public cold chain practice.
