After calling out to the woman, they decided to open the door with a coin and found the lifeless body inside.
Emergency services arrived at the scene but the woman could not be saved.
Police said the autopsy revealed no evidence of foul play.
An investigation into the salon found there were no faults with the sunbeds.
"We express our deepest condolences to the relatives," a spokesperson for the salon said.
The results of a toxicological study are pending.
It's not the first time someone has died in a tanning salon.
In the UK, a bride-to-be collapsed and died in a tanning cubicle in Manchester.
Jenna Vickers was found after the manager broke in and tried to save her.
She had told her friends she was injecting herself with a tanning product.