As FLAASH module multiplies the output (surface reflectance data) by 10,000 omitting decimals for faster calculations and lower file size, we should apply this equation:
(B1 le 0)*0+(B1 ge 10000)*1+(B1 gt 0 and B1 lt 10000)*float (b1)/10000
le means less than or equal
ge means greater than or equal
gt means greater than
lt means less than
The resulting surface reflectance data will lie between 0 to less than unity (0 to <1) suitable for further image spectrometry and comparable with most spectral libraries.
I hope that helps