Nothing is truly absolutely safe. When engaging in sub-ohm vaping, it is important to have a good understanding of Ohm’s law and to know your batteries’ capability since sub-ohm vaping taxes a unit’s batteries pretty heavily, heightening the risk of battery damage – the main risk for vaping safety.
With that said, you should always gain prior knowledge about your specific device and adhere to the manufacturer’s recommended wattage range for use with your sub-ohm tank’s coil to avoid electrical fault.