A laborer was steam cleaning a scraper used in a street paving project. The hydraulically-controlled bowl apron of the scraper weighing approximately 2,500 pounds had been left in the raised position. It had not been blocked to prevent it from falling. The apron did fall and the employee was caught between the apron and the cutting edge of the scraper bowl. Blades of scrapers, bulldozers and similar equipment should be either fully lowered or blocked when being repaired or not in use. Hydraulic equipment such as this can unexpectedly fall or be activated unless it is blocked from movement.