LEBANON, VA., JULY 14 -- A timed car bomb exploded in the parking lot of a Pittston Co. headquarters this morning, and two workers were shot and wounded in a separate incident at a West Virginia mine, the latest in a series of violent incidents that have marred the 15-week-old dispute between the United Mine Workers and Pittston. The bomb exploded about 9:20 a.m. at the rear of a truck owned by a replacement worker who had been hired by Pittston, officials said. State Police 1st Sgt. Mike Frank said no one was injured in the blast, and that no arrests have been made. The bomb taped to the right rear axle of the International Scout was made of a small amount of black blasting powder and was detonated "with some type of timing mechanism," Frank said. He said the vehicle was destroyed. About an hour earlier, two employees at a non-union coal mine were struck by gunfire today in Mingo County, W.Va., authorities said. Two Hampden Coal Co. employees at the Gilbert mine were replacing windows protecting a camera surveillance system that had been splashed with paint when they were hit by shotgun pellets about 8:05 a.m., State Police spokesman Ric Robinson said. One of the workers was struck several times in the face and the other was hit in the shoulder, Robinson said. The workers' names and conditions weren't immediately available, he said. The United Mine Workers' strike involving 1,900 Pittston employees from Virginia, West Virginia and Kentucky began April 5. Pittston has been hiring replacement workers, who have been the targets of almost daily acts of intimidation, much of it in the form of damage to their property. About 37,000 other miners walked off the job on June 12 in support of the Pittston strikers. Their walkouts are not authorized by the union and are called wildcat strikes. Union miners east of the Mississippi are scheduled to return to work Saturday after a five-day cooling off period ordered by UMW President Richard Trumka to ease tensions in the coal fields. In a letter to West Virginia Gov. Gaston Caperton, E. Morgan Massey, president of the A.T. Massey Coal Co., accused Trumka of using the cooling-off period to conduct a campaign of orchestrated terrorism." Caperton cut short a trip to South Carolina and returned home Thursday. The governor went to South Carolina to attend an economic conference, said spokesman Steve Cohen.