Life Support Technician (LST) Exam Prep
Free practice questions

Free LST Practice Questions

10 exam-style questions with answers and explanations, straight from our 1,050-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.

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Question 1

A saturation chamber is being held at a storage depth of 231 fsw. What is the absolute pressure inside the chamber?

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Correct answer: D - 8.0 ATA

Question 2

An LST must blend a breathing gas that will deliver an oxygen partial pressure of 0.45 ata at a storage depth of 300 fsw. What oxygen fraction is required?

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Correct answer: D - 4.46%

Question 3

A helium quad is charged to 2,400 PSIG at 70°F and left on deck, where its temperature rises to 100°F. Assuming no gas is drawn off, the quad will read approximately:

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Correct answer: C - 2,537 PSIG

Question 4

A chamber CO2 analyser reads 0.05% actual at a storage depth of 300 fsw. Expressed as a surface equivalent value, this reading is:

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Correct answer: D - 0.50% SEV

Question 5

Which gas law explains why helium moves across a pressure gradient more rapidly than nitrogen at equivalent partial pressure?

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Correct answer: B - Graham's Law, under which diffusion rate varies inversely with the square root of molecular weight

Question 6

A diver reaches the surface and within four minutes presents with sudden unconsciousness and one-sided weakness. The most likely diagnosis is:

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Correct answer: B - Arterial gas embolism, arising from pulmonary overinflation on ascent

Question 7

Pulmonary oxygen toxicity, as distinct from central nervous system oxygen toxicity, is characterised by:

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Correct answer: D - Cumulative exposure at moderate partial pressures, tracked in UPTD

Question 8

During compression to a storage depth of 650 fsw on heliox, a diver reports tremors, dizziness and nausea. The LST should recognise this as:

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Correct answer: A - High Pressure Nervous Syndrome, mitigated by slowing the compression rate

Question 9

A diver surfaces reporting pain in the left shoulder. The pain is not relieved after 10 minutes at 60 fsw on oxygen. The indicated treatment table is:

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Correct answer: C - Treatment Table 6, the standard schedule where pain is unrelieved at 60 fsw

Question 10

Which oxygen partial pressure range represents the limits of safe diver exposure within a saturation chamber?

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Correct answer: A - 0.16 to 1.25 ata

That's 10 of 1,050

The full bank has 1,040 more LST questions with explanations.

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