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There are a number of potential electrical hazards in a typical home. Most work done by professionals in the last 25 or 30 years should be safe even today, but one or two exceptions to that rule of thumb do exist.
If your home was built more than 25 years ago then there are elements to your electrical system that you should consider having inspected by a professional electrician. Not least is the possibility that your panel is simply too small for your home's needs
The next item to concern you should be the actual brand of your service panel and any sub-panels in your home. Again, anything less than 25 years old should be safe, assuming that it was competently installed. (Modern circuit breakers do fail, but new ones are designed to "fail safe", that is, to just stop passing electricity.)
Fuses are the oldest concept and indicate that you should look over your entire system. A fuse service will certainly not be large enough to support a modern home safely. If you want to keep the fuse panel, be CERTAIN to use only the correct ampacity fuses for each circuit. Many fires have started because residents used a larger fuse than was correct.
There are three common antiquated circuit breaker panels, two of which present real hazards, in particular a failure to trip "off" when overloaded, which is the prime purpose of a breaker in the first place.
Zinsco is very common and is long out of production. Replacement breakers are available, but the history of Zinsco breakers failing to trip when overloaded or the entire panel simply bursting into flames underlies the urgency of replacing the panel. See this unhappy picture.
Federal Pacific "Stab Lock" panels and breakers are every bit as hazardous. It is a remarkably poor design and no new panels have been installed in decades. These breakers have been proved in repeated tests to FAIL in their main purpose: shutting off the power in an overload. Regrettably, they look at a first glance much like any good modern breaker. The breaker pictured has suffered a relatively mild (for a Stab Lock) failure that still could burn down a house.
Bulldog's "Pushmatic" breakers are the third in our list of archaic breaker concepts. However, the design is somewhat less hazardous; they tend to work as designed. They are, however, difficult and expensive to expand. If you need to add a circuit for air-conditioning, as an example, it may just not be possible to use this panel.
As critical to your safety is the execution of the grounding system. The rule stated above, that work done competently in the last few decades should be safe, still applies. But standards were much looser forty and fifty years ago, and methods were used then that would not be acceptable today. It makes sense to ask a professional to inspect your grounding system the next time you have an electrician working on your home.
As the electricity exits your panel and enters your home, it is traveling in wires, which have insulation. Wire is almost universally made of copper, except for a brief period in the late '60s to mid '70s when the cost of copper forced the use of aluminum. If your house has aluminum wire in it, you at the minimum need to understand its hazards, which are many, and you might consider replacing it, especially if you are doing any other major work on the house.
Older wire, and especially older insulation and wiring methods are the other major hazard to your home beyond the panel that you should be aware of. Knob and tube is just about the oldest wiring system, and has been out of use since the mid 1920s. It has no provision for a ground, and the wire is designed to be suspended in free air. You will find it in attics and walls with insulation blown over it, which causes it to run hotter than it should: a fire hazard.
If your home was wired with conduit, and many homes are, then you are largely in luck, as even if the wire in the conduit is dated and its insulation is breaking down (common) the wire can be replaced with minimal need to break open walls; fresh wire can simply be pulled into the conduit to replace the old wire.
Until a few decades ago the most common wire was "rag wire". This had a rubber-like substance wrapped in cloth. It is rated to perform in a relatively low temperature environment, and tends to deteriorate very badly over time. If you have ever replaced an outlet or a ceiling light and found the insulation simply crumbling away, you were working with rag wire. It is essentially the same stuff that knob and tube was wired with.
Rag wire was run down conduit and also incorporated into cables of various sorts, many of which did not provide for a ground (if you see a receptacle with only two blades, you may not have any ground available). A common and sensible upgrade of any older home that has rag wire and conduit is to simply pull in modern wire.
Modern wires and cables are insulated and sheathed in high-tech thermo-plastics that are extremely resistant to heat, and have very long lives even under fairly heavy use. If any alterations are made to your home's wiring it will almost certainly be done in this modern material which can experience 90 degree centigrade (nearly the boiling point of water) without breaking down.
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