Abstract: On November 20, 2007, Employee #1, an equipment operator, was repairing a natural gas line leak in Fresno, California. Employee #1 was replacing a section of class Number 3 residential polypropylene plastic service line, which had 1 in. in diameter and 0.090-in. wall thickness. The gas line was damaged by an electrical crew, while removing tree roots to access the electrical conductors in a joint service trench. The gas line was damaged with a shovel causing a blowing gas leak. The gas line had pressure of 50 PSI and was covered with dirt to muffle the noise. A gas crew, together with Employee #1 and a gas construction foreman, were dispatched to repair the leak. An attempt was made to enlarge the excavation with a backhoe, but the roots caused the ground to rise as a unit. To mitigate further property damage the crew decided to cut away the roots using a saw. An attempt was made with a hand saw, but progress was slow, thus the crew decided to use a Bosch 18 volt cordless reciprocation saw. Employee #1 got into the excavation for positioning and energizing the saw, which ignited the flammable gas. Employee #1 got out from the excavation with only a flash burn to his face and irregular heart beat. He was hospitalized with nonserious injuries to his face and heart condition, which was determined as nonoccupational. Both, Employee #1 and the gas construction foreman were not aware that a cordless power tool would be an ignition source. Root cause for this event was the use of a spark producing power tool, which was an ignition source, in a flammable atmosphere.