Normally Closed Optoisolators
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.

However, note that if the opto fails short then that will open the transistor.

The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.







simulate this circuit &ndash; Schematic created using CircuitLab