Investigators say the cause of a fire that killed several animals at the Henry Doorly Zoo can't be pinned down it but was related to an infrared heater in a barn.

The barn fire happened on January 15th. Seven of the zoo's herd of 12 female Nile lechwe and two sandhill cranes died in the blaze.

Investigators say that the incident was unquestionably linked to an infrared heater hung from the ceiling in the southwest stall of the barn but how it happened can't be determined.

As a precaution, all similar heaters used at the zoo were taken down for inspection, as was the heat shielding that protects the ceiling and wood framing from the heaters.

Zoo officials say they found some incidences in other barns where the heat shielding had warped over time allowing hot gases to penetrate upward. They say they believe that this same warping had happened in the lechwe barn and could possibly have been the cause of the fire.

All of the valves and controls on the heaters have been replaced, as has the heat shielding in all of the barns. The new shielding is five-times thicker than the old and contains a thick layer of glass foam.