It is very important topic that what are hazards in digital circuit ? When you design any digital circuit you have to consider the hazards in digital circuit. If we want to find the answer of question that what are hazards in digital circuit? Then the basic thing we should give attention that for asynchronous sequential circuits it is important that undesirable glitches on signals should not occur. We should be aware of the all possible sources of glitches and we have to ensure that the transitions in a circuit will be glitch free. Those glitches created by the structure of a given circuit and also the propagation delays in the circuit are referred to as hazards.
As we know any digital circuit can generate output only two state high (1) and zero (0). so due to any input change and for some combination of propagation delays, output of that digital circuit may momentarily go to 0 when it should remain a constant 1. Then we can say the network has a static 1-hazard. Similarly, if any digital circuit give output may momentarily go to 1 when it should remain a constant 0, then we say that the digital circuit has a static 0-hazard. Static 0- and 1-hazards can be eliminated by adding additional gates to the network to produce the missing 1-terms and 0-terms.
The above phenomenon is under static hazard. But in any digital circuit we can see two types of hazards
1 Static Hazard
2 Dynamic hazards
Now question is what is a dynamic hazard? Now imagine if any digital circuit if when, the output is supposed to change from 1 to 0 (or 0 to 1), the output may change three or more times, we say that the digital circuit has a dynamic hazard. Dynamic hazards are not easy to detect nor easy to deal with. The designer can avoid dynamic hazards simply by using two-level circuits and ensuring that there are no static hazards.