Separate 1,2,3 into individual 1 and 2 and 3

Can anybody help me, I have a session like this:

$_SESSION['SES_SA'] = 1,2,3

Then I want to use it like this:

if($_SESSION['SES_SA']=="1"){
  ......
}
elseif($_SESSION['SES_SA']=="2"){
  ......
}
elseif($_SESSION['SES_SA']=="3"){
  ......
}

Is it posible?