Life-cycle analysis practice questions.

A design team is recording every input and output of a kettle production system in kilograms of material and megajoules of energy, without yet judging what those flows do to the environment. Which phase of a life-cycle analysis is being carried out?

• Goal and scope definition
• Impact assessment
• Interpretation
• Inventory analysis

Answer: Inventory analysis

Inventory analysis only quantifies the flows crossing the system boundary; converting those flows into effects such as global warming potential is the later impact assessment phase. Goal and scope definition comes first and fixes the boundary and the functional unit.

A life-cycle analysis compares a warm-air hand dryer with paper towels in an office washroom over ten years. Which quantity should be chosen as the functional unit of the study?

• One kilogram of product material in each system
• One year of electricity supplied to the washroom
• Drying one pair of hands, repeated 100 000 times
• One installed dryer and one full case of paper towels

Answer: Drying one pair of hands, repeated 100 000 times

The functional unit expresses the service delivered, so both systems must be measured against the same amount of useful work rather than the same mass or the same number of devices. Comparing one dryer with one case of towels compares unequal quantities of service.

A solid oak bookcase is flat-packed, assembled by the customer and then used for thirty years without consuming any energy in service. Which life-cycle stage will dominate its total energy demand?

• The use phase, because thirty years in service is by far the longest stage of the life cycle
• Material acquisition and processing, because kilning and machining the timber dominate
• Distribution, because solid oak is heavy and is trucked over long distances
• End of life, because landfilled timber releases methane as it decomposes

Answer: Material acquisition and processing, because kilning and machining the timber dominate

A product that uses no energy in service carries almost all of its burden before it is sold, so kilning and machining decide the total. Length of service and shipping mass stretch or load a stage without adding much energy to it, and methane from landfill is a global warming impact rather than an energy demand.

Replacing a fossil-based polymer with a crop-based one lowers the global warming potential of a bottle but raises its eutrophication and land-use figures. Which feature of life-cycle analysis does this result illustrate?

• Burden shifting between impact categories
• An expansion of the system boundary beyond the factory gate
• A change in the chosen functional unit
• Allocation of shared flows between two co-products

Answer: Burden shifting between impact categories

Several impact categories are reported precisely because an improvement in one is often paid for in another, so reading the carbon figure alone hides the trade-off. Burden shifting is a genuine result of the study, not a methodological mistake.

A sales report describes a games console as moving from growth into maturity, while an environmental report describes the same console as moving from manufacture into use. Which statement identifies the two models correctly?

• Both reports describe stages of a life-cycle analysis seen from two departments
• Both reports describe the product life cycle, one in market and one in physical terms
• The sales report uses life-cycle analysis and the environmental report uses the product life cycle
• The sales report uses the product life cycle and the environmental report life-cycle analysis

Answer: The sales report uses the product life cycle and the environmental report life-cycle analysis

The product life cycle tracks sales over time in a market, while life-cycle analysis quantifies environmental burden from material extraction to disposal. Confusing them makes the market phase decline look like an end-of-life stage, which it is not.

A sawmill cuts logs into planks and sells the sawdust to a pellet plant. Before either product can be given a life-cycle figure, the electricity and the log input of the mill have to be divided between them. Which methodological step of a life-cycle analysis is this?

• Normalisation, expressing a result against a chosen reference figure
• Characterisation, converting a measured flow into an impact figure
• Allocation, dividing a shared process between two co-products
• Sensitivity analysis, testing how far the result depends on one assumption

Answer: Allocation, dividing a shared process between two co-products

A process that serves two products cannot be charged to either one alone, so the study must declare a rule - by mass, by energy content or by economic value - and a different rule gives a different published figure. Allocation is carried out during inventory analysis; only the rule chosen is fixed in the goal and scope phase and reported with the result.