Fairchild's datasheet and it says so explicitly: "The optoisolator should not be used to drive a load directly. It is intended to be a trigger device only." But then Motorola, I mean On Semiconductor, tells us that, "Zero-crossing optocouplers can be used to switch inductive loads at currents less than 100 mA (Figure 24)" [p.162].
What I have in my parts bin are a number of MOC3021. Since these can pass around 100mA [p.124] continuously, with a peak current of 1000mA (pulse width of 1ms, 120 pulses per second), there shouldn't be a problem if the load does not exceed these maximums. The MOC3021 is a random-phase and not zero-crossing optoisolator but I figure if I just close my eyes, ignore the difference and wish upon a star then everything will be alright.
The load I need to switch are 24VAC mini relays which in turn will switch 220VAC loads. Measured maximum current of the relay @24volts is 46mA. Connecting a 24VAC source and a relay in series with the triac output presented no problems--turning the MOC3021's LED on and off switched the relay. I then wondered if the optoisolator could drive two relays in parallel. They switched on fine, but when I powered down the LED the relays remained on. They just wouldn't turn off.
To try and remedy this I placed a 0.1uF ceramic capacitor across the triac. That immediately got rid of the latching. I tweaked the snubber and replaced the cap with a 0.01uF and a 1Kohm 1/4W resistor. No latching problems. However, decreasing capacitance to 1nF or increasing resistance to tens of kilohms reduced snubbing to a point that latching would occur.