Abstract: At Approximately 7:30 AM, an employee (EE#1) of Dunn's Designer Pool sustained 2nd and 3rd degree burns to 51of his body that included the chest, back and both legs. An employer representative for Dunn's Designer Poolreported this accident to the San Bernardino District Office on the same day at 8:45 AM. Dunn's Designer Pool is a pool contractor. EE#1 went into an underground vault to bleed a line leading to the heater. The heater warms up the water in the spa. EE#1 after bleeding the line he exit the underground vault to check the water in the spa to make sure that it was heating up. EE#1 then went back and entered the underground fault to turn off the valve for the heater. EE#1 then began exiting the underground fault when there was an explosion. EE#1's body was half way out the vault when an explosion occurred. The explosion threw EE#1 approximately five feet into the air causing EE#1 to land on the steel grate (opening) of the underground vault. EE#1 right leg was hanging in the vault when he landed. The cause of this accident was the employer did not test conditions in the permit space to determine if acceptable entry conditions exist before entry is authorize to begin.