A common example of needing icons to be accessible is when they’re used as buttons eg. search button, left and right navigation buttons etc. To do this, add the css:

.fa span{
 text-indent: -9999px;
 display: inline-block;
}

and in your html just add the text in a span inside the icon like so:

<i class="fa fa-search><span>search</span></i>