As we move into Part 3 of our discussion about the usefulness of mechanical safeties on handguns, there is one additional point to keep in mind: The primary reason for having safeties on firearms in the first place is to prevent the firearm from being discharged when you don't want it to be. Although that seems obvious on the surface, there are actually two needs to consider. One is to prevent you, the intended user, from having an unintentional discharge. The other is to prevent someone else from firing the gun, whether intentional or not.
Both of these considerations carry particular importance for law enforcement officers, as there is always at least one gun present as they go about their duties... their own. It is not just essential that the firearm be safely carried and readily available for use, it must also be secure from being seized and used by others against the officer or someone else. This is the delicate balance that must be achieved through proper equipment selection and appropriate training. Indeed, the current choices in security or retention holsters are the best they have ever been. This is so because too many officers have been the victims of having their guns snatched from their holsters by determined or desperate attackers. Since this is not a discussion about holsters, I'll simply acknowledge that a good duty holster is an essential part of any officer's safety system for carrying a firearm. For now, let's concentrate on what happens when the gun leaves the holster.
Over the years, there have been many mechanical devices on handguns that have functioned as safeties in some manner. The only ones that have any usefulness on a self defense handgun are those that can be quickly activated or deactivated while the user maintains a firm shooting grip on the gun. Because of this, the typical type of safety on a service pistol today is the Thumb Safety, so named because it can be manipulated with the thumb of the shooting hand.
There are generally two categories of these, frame mounted and slide mounted. The frame mounted safety is usually simply an "on-off" switch. Typical examples of this type would be the Colt 1911 pattern pistols, the new Smith and Wesson M&P pistols (as an option), and the Ruger SR9. It either prevents the gun from firing or it doesn't. The slide mounted safeties often double as both a firing safety and as a de-cocker, which allows the safe lowering of the hammer from the cocked, single action firing position. The most common of the police service pistols with such systems are the Beretta Model 92 style guns, the Ruger P series pistols and the traditional design Smith and Wesson auto-loaders, such as the Model 5906, 4006, etc. If you have been issued a pistol with a thumb safety, it is probably because your agency is concerned about the two issues I mentioned in the first paragraph, no accidental discharges and no officers getting shot with their own guns. Does using such guns accomplish those goals? Generally, yes. Do they do so by virtue of their presence alone? Not necessarily. Let's look at the pluses and minuses.
The UP Side
One of the most important advantages of having a pistol with a mechanical safety is that it takes some knowledge on the part of the user to turn it on and get it into action. This should not be a problem for any officer, who should have sufficient training in manipulating the safety so that deploying the gun in firing condition is reflexive. As the decision to fire is made, the safety should be smoothly and quickly deactivated. Likewise, it should be smoothly and quickly reactivated when the need to fire has passed. On the other hand, any unauthorized person who gains control of the weapon may not know how to quickly begin firing the gun, giving the officer a chance to regain control of the pistol before it is used against him or her. If control is not possible, then perhaps other tactics, such as accessing a backup gun, deploying other weapons or moving to cover can be accomplished. It may take only a few seconds for the bad guy to figure it out, but officer's lives have been saved by quick reaction in those precious seconds. Operating controls that are proprietary to the gun and user are reason enough to at least consider whether your gun should have a manual safety.