Vinyl chloride finds its major application in the production of PVC. It is volatile, so the primary exposure is via inhalation as against food or water with occupational hazards being highest. Prior to 1974, workers were commonly exposed to 1,000 ppm vinyl chloride, causing "vinyl chloride illness" such as acroosteolysis and Raynaud's Phenomenon. The symptoms of vinyl chloride exposure are classified by ppm levels in ambient air with 4,000 ppm having a threshold effect. The intensity of symptoms varies from acute (1,000-8,000 ppm), including dizziness, nausea, visual disturbances, headache, and ataxia, to chronic (above 12,000 ppm), including narcotic effect, cardiac arrhythmias, and fatal respiratory failure. RADS (Reactive Airway Dysfunction Syndrome) may be caused by acute exposure to vinyl chloride.