Lasers Revision Seminar

Question 1

What is the MPE and NOHD? (2 marks)

Answer 1

MPE = maximal permissible exposure = duration that tissue can be exposed to laser light before damage will occur, varies with tissue, type of laser, power etc

NOHD = nominal ocular hazard distance = minimal distance required for to be below the MPE

Question 2

What is the equation for NOHD? (1 mark)

Answer 2

NOHD = (2/theta)*(P/(PI * MPE))^0.5

P is power in watts and theta is angle in radians.
Gives NOHD in metres.

Question 3

Give three safety measures required when using a laser? (3 marks)

Answer 3

• Appropriate eye protection
• Signage
• Remove reflective objects from room if possible
• Restrict access if needed

Question 4

What is the most common feature of laser accidents? (1 mark)

Answer 4

Inappropriate eye protection.

Question 5

How does using a fibre affect the nominal ocular hazard distance? (1 mark)

Answer 5

It decreases the NOHD as the divergence is much greater.

Question 6

What implication would a very short NOHD have on safety practice and PPE? (2 marks)

Answer 6

If the NOHD is short the may not require eye protection as there is minimal risk of damage to eye.

We may not need to classify the area.

Question 7

How often should a laser audit be carried out and what should be inspected? (5 marks)

Answer 7

• Annual inspection.

- Check eyewear, signage, local rules, fire risk, electrical risks, approved user lists up to date…