Could anyone help me with a statistical process control problem i have?

I am measuring a process which gives a measured value range from 0 to infinite, although in practice values are mostly 0 with a few outliers typically reaching a max value of 10.

The measured values are never below 0 so i have a heavily skewed distribution with 0 being the most common value, typically the standard deviation will be about 0.4 with a mean of 0.2. I'll have 40-80 samples per month.

For my process to remain in control i need to show that 90% of my measurements have a value of less than 1 with a 95% confidence. What is the best way of doing this? I'd like to understand how to work this out.

Any help would be most appreciated.

thanks

Steve