Can they? Yes.
It's up to the user. When used with most players, yes, if listened to for more than a half hour a day a full volume. These headphones will produce between 98 and 105 dB SPL when driven with one milliwatt at their nominal impedance. For a 32-ohm impedance earphone, which most are, that is 0.187 volts rms. The standard "line" output for most players is 2.0 volts rms. Doing the math says that, for broadband signals such as music, an earphone with a sensitivity of 100 dB SPL @ 1 mw can produce 110 dB SPL. That's an unsafe level regardless of how long you listen. Therefore, my advice is that if you are going to use any earphone for extended listening, keep the input level down. For most smart phones and players, that means at slightly less than 50% volume.
Some earphones say they are safe, but except for one, they just decrease the sensitivity. With enough voltage, they can reach high levels as well. I know, I have tried them.
Here's a good way to adjust volume to a safe level: Put the earphones in and seat them so that they are sealed. Now hum at a normal level of vocal effort - that is at the same level at which you normally talk (assuming you don't normally yell). Now adjust the level of the music so that the sound of your humming blends with but is not overpowered by the music. The subsequent listening level should be safe for as long as you wish to listen. If you notice you aren't hearing enough bass, lower-frequency, sounds, either get a better seal of the earphone in your ear or buy a better earphone.
