Three underground utility workers in Florida died Monday after entering a confined space without the proper protective equipment.

The incident, which occurred in Key Largo, Fla., began when the first man removed a manhole cover, entered a 15-foot-deep drainage hole and became unresponsive, according to news reports.

The second worker entered with the intention of saving him but also lost consciousness. Likewise, a third man climbed into the hole was overcome by fumes. All three workers perished. None were wearing any respiratory protective equipment.