Understanding Toxic Chemicals: Concentrations and Metrics

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What does one part per million (ppm) represent in terms of distance?

1 kilometre in 1,000 metres

1 metre in 1,000 kilometres (correct)

1 millimetre in 1,000 kilometres

1 centimetre in 1,000 metres

What is the purpose of Threshold Limit Values (TLVs)?

To measure the effects of toxic substances on the environment

To determine the minimum amount of toxic substances in the air

To establish a safe concentration of substances for most workers (correct)

To identify the most toxic substances in the workplace

What is the time period for which the TLV-TWA is calculated?

A normal 8-hour workday (correct)

A normal 4-hour workday

A normal 24-hour workday

A normal 12-hour workday

What is the percentage of people who may experience discomfort from some substances at concentrations at or below the threshold limit?

A small percentage Signup and view all the answers

What is the volume of liquid in which 1 millilitre is equivalent to 1 ppm?

1,000 litres Signup and view all the answers

What is the area of the square in which 1 square centimetre is equivalent to 1 ppm?

100 square metres Signup and view all the answers

When is the 8-hour TLV referred to?

When TWA is not indicated Signup and view all the answers

What should you do when dealing with a serious ammonia leak or spill?

Use a water spray or fog to reduce the gas cloud Signup and view all the answers

What type of extinguishers are suitable for fighting fires involving ammonia?

Carbon dioxide and powder extinguishers Signup and view all the answers

What should you do with ammonia cylinders in a fire?

Move them away from the fire area if it is safe to do so Signup and view all the answers

What happens when pressurized ammonia containers are exposed to fire?

They rupture and release ammonia gas Signup and view all the answers

What is the minimum concentration of ammonia in the air that can cause moderate irritation of mucus membranes?

5–15 PPM Signup and view all the answers

What is the characteristic of ammonia gas that makes it harder to extinguish fires?

It is not readily ignited Signup and view all the answers

What is the maximum concentration of ammonia in the air that can be fatal in 30 minutes?

400 PPM Signup and view all the answers

What is the characteristic of carbon dioxide gas?

It is a colourless, odourless gas Signup and view all the answers

What is the primary consideration when dealing with two or more hazardous substances that have a similar toxicological effect on the same target or system?

The combined effect of the substances Signup and view all the answers

What is the significance of a dose greater than 1 in the equation for determining the combined TLV?

The TLV for the mixture has been exceeded Signup and view all the answers

What is the Median Lethal Dose (LD 50) a measure of?

The dose of a toxic substance that is fatal for 50% of a test population Signup and view all the answers

What is the purpose of the Threshold Limit Value – Ceiling (TLV‑C)?

To determine the concentration of a toxic substance that should not be exceeded during any part of the working exposure Signup and view all the answers

What is the Median Lethal Concentration (LC 50) a measure of?

The concentration of a toxic substance that is fatal for 50% of a test population Signup and view all the answers

What is Immediately Dangerous to Life and Health (IDLH)?

A condition posing an immediate threat to life or health Signup and view all the answers

What is the equation for determining the combined TLV?

𝐶1 𝐶2 𝐶𝑛 + +⋯ = 𝐷𝑜𝑠𝑒 𝑇1 𝑇2 𝑇𝑛 Signup and view all the answers

What is the significance of the Threshold Limit Value (TLV)?

It is the concentration of a toxic substance that should not be exceeded during any part of the working exposure Signup and view all the answers

What is the minimum percentage of oxygen that should be present in the atmosphere at a workplace?

19.5% Signup and view all the answers

What is cross sensitivity in gas detection equipment?

The response of a sensor to a gas that is not the target of the sensor Signup and view all the answers

What is the effect of oxygen deficiency at 15% O₂ in the atmosphere?

Dizziness, buzzing noise, rapid pulse, headache, blurred vision Signup and view all the answers

What is the response time of a gas detection instrument?

The ability to react to its specific gas in the time specified Signup and view all the answers

What is the chemical symbol for propane?

C₃H₈ Signup and view all the answers

What is the limit of detection (LOD) of a gas detection instrument?

The lowest quantity or concentration of a substance that the instrument can register within a margin of confidence Signup and view all the answers

What is precision in gas detection?

The degree to which repeated measurements under unchanged conditions show the same results Signup and view all the answers

What is the primary hazard of propane vapour?

It is heavier than air and can accumulate in low places Signup and view all the answers

What is the explosive range of propane?

2.4%–9.5% Signup and view all the answers

What is noise or drift in gas detection?

How much readings fluctuate when the quantity or concentration of a substance stays the same Signup and view all the answers

What is dynamic range in gas detection?

The ratio between the largest and smallest possible signals Signup and view all the answers

What happens when liquid propane is converted to vapour?

It will expand to about 270 times its liquid volume Signup and view all the answers

What is the primary effect of propane on humans?

It can cause an oxygen-deficient atmosphere resulting in asphyxiation Signup and view all the answers

What is a common interference in gas detection equipment?

All of the above Signup and view all the answers

Why is propane commercially scented?

To detect leaks or escaping gas Signup and view all the answers

What is important to follow when using gas detection equipment?

The manufacturer's specifications for application and use Signup and view all the answers