Final answer:
OSHA requires that portable fire extinguishers are visually inspected monthly to ensure they are in operable condition and have not been damaged.
Step-by-step explanation:
According to OSHA regulations, portable fire extinguishers should be visually inspected monthly. This is important to ensure that the extinguisher is in its designated place, has not been damaged and appears to be in operable condition. This means that Option 1: Monthly, is the correct answer for the frequency of visual inspections for portable fire extinguishers. Knowing the location of safety equipment like fire extinguishers and eyewash stations is essential for laboratory safety.