Which statement describes Class 4 lasers?

• A. They are safe to view without protection
• B. They are high-power lasers hazardous to view under any condition and can cause skin and fire hazards
• C. They emit only infrared and are safe
• D. They are never hazardous

Answer: (B)

Class 4 lasers are at the highest risk level for laser safety. They deliver enough power to cause immediate eye injuries and skin burns, and they can ignite flammable materials. Because of this, viewing the beam is hazardous under any condition, including diffuse reflections, not just direct exposure. This is why safety measures are so stringent: enclosed beam paths, interlocks, controlled access, and eye protection rated for the specific wavelength and power. The statement captures these essential hazards—high power, eye danger under any viewing condition, and potential for skin burns and fires.

The other descriptions don’t fit because Class 4 lasers aren’t safe to view without protection, aren’t restricted to infrared or “safe” wavelengths, and are indeed hazardous in typical use scenarios.