Safety is a spotty thing when you refer to something holding a bunch of highly flammable fluids.
In an emergency it can be used, but things that use fire have three basic needs to work
Heat, Fuel, and Oxygen.
With that in mind after starting it the fuel starts to burn, this leaves Oxygen being consumed.
Also you need to consider what exhaust the kerosene is putting out.
The main issue is the carbon monoxide. I suggest you install a CO detector too before using if you don't already have one.
So while it is likely not going to kill you if you use it for a short time, it is definitely not all too safe for indoor use.
If it had an air intake you want to connect that to outside your house and make sure it won't be obstructed by snow. If you have an exhaust output you want to connect that outside the house to somewhere that is not near the intake source. If you have a picture of the heater more specific info can be given.
There are also things called fume hoods that could be useful not only for this but also other DIY projects.
It is not unsafe, but safe may not be the right word. If installed correctly it would not be unsafe to use correctly.
However anytime there is fuel within your living space it could be a fire risk.
It may also be against your local building codes. Check them out before you install anything. It may also invalidate your home insurance.
"Fire Departments: It may be useful to contact your local fire department at their nonemergency telephone number to find out what their response will be to a CO alarm in a residence. Your local fire department may also offer free home fire safety inspections that would include checks of potentially CO-generating equipment." - from http://www.carbonmonoxidekills.com/carbon-monoxide-advice/
This is no little thing, it is like asking how your gun barrel should be cleaned. The wrong advice could kill you.\
People rarely ask how to correct internal bleeding and surgery methods but they will ask for advice about something that kills just as many people.
You get medical advice from a doctor or other health practitioner.
You should be getting advice on heating systems from a HVAC certified person or applicable engineer.