Workplace ventilation and hazard control in construction require preventive measures, protective equipment, and monitored air quality. Adequate preventive measures must be taken in building or other construction work where employees may be exposed to chemical, physical or biological hazards likely to endanger health. Such measures include substitution of hazardous substances where possible, technical controls, and, where those are not feasible, other effective safeguards such as personal protective equipment and protective clothing supplied free of charge. Comparable protection is required for toxic or harmful substances, oxygen deficiency, flammable atmospheres, heat stress, cold or wet conditions, and workplace ventilation, temperature, humidity and tunneling safeguards.