Question 1 of 5: LCA Fundamentals – Boundaries, Life-Cycle Phases, Impact Assessment, Benchmark Compounds

Question 1: LCA Fundamentals – Boundaries, Life-Cycle Phases, Impact Assessment, Benchmark Compounds (28 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) System boundaries and the functional unit

An LCA's conclusions are only as trustworthy as the boundary drawn around the system under study and the basis chosen for comparing alternatives. The system boundary fixes which life-cycle stages, unit processes, and geographic/temporal scope are included in the inventory — common choices are cradle-to-gate (raw-material extraction through the factory gate), gate-to-gate (a single process step), and cradle-to-grave (extraction through end-of-life disposal, reuse, or recycling). The functional unit is the quantified basis of equivalent service on which competing systems are compared, and it must reflect the service each alternative actually delivers, not a convenient physical count of one of them.

Worked example — LED vs. incandescent light bulbs. If the boundary is drawn narrowly as cradle-to-gate manufacturing and the functional unit is naively taken as "one bulb produced," an incandescent bulb (a simple tungsten filament, glass envelope and base, requiring modest processing energy) looks far less energy- and material-intensive to manufacture than an LED bulb (a doped-semiconductor die, phosphor coating, aluminum heat sink and driver electronics, all of which carry a materially higher embodied energy and rarer-material burden per bulb produced). A study stopped there would recommend incandescent outright on a "per bulb manufactured" basis. But an incandescent bulb typically delivers roughly 1,000 hours of service and converts under 5% of its input electricity to visible light (the rest is waste heat), while an LED delivers 15,000–25,000 hours at roughly five times the luminous efficacy. Extending the boundary to cradle-to-grave over an equal service period (e.g. "provide 20,000 hours of equivalent illumination," the correctly re-scaled functional unit, requiring roughly twenty incandescent bulbs and their associated replacement/packaging/ transport burden versus essentially one LED bulb) and including each alternative's in-use electricity draw over that period reverses the per-unit conclusion entirely: the dominant life-cycle burden for incandescent lighting is use-phase electricity consumption, not manufacturing, and the LED's higher manufacturing burden is repaid many times over by its use-phase savings. This demonstrates that boundary and functional-unit selection are not bookkeeping details: they determine which alternative appears superior, and a comparison that stops at the factory gate, or compares "per bulb produced" instead of "per unit of illumination-hours delivered," is not defensible engineering judgement — a concern directly relevant to the federal and provincial incandescent-phase-out policies enacted across Canada on the strength of exactly this cradle-to-grave comparison.

(b) Life-cycle phases

The general phases associated with a product's development and distribution are: (1) raw material acquisition (extraction/harvesting of virgin or recycled feedstocks); (2) materials processing (converting feedstocks into engineering materials, e.g. refined silicon, phosphors, aluminum); (3) manufacturing/assembly of the product itself; (4) distribution/transportation to the point of use; (5) use phase (in-service operation, including any maintenance or replacement); and (6) end-of-life management (collection, recycling of recoverable materials, or landfill/hazardous disposal).

Continuing the lighting example, consider the use phase. Inputs to investigate are the grid electricity consumed over the bulb's rated life (itself dependent on the local generation mix — hydro-dominant Canadian grids carry a far lower per-kWh carbon burden than a coal-heavy grid) and any heating/cooling interaction (incandescent waste heat offsets space heating in winter but adds to cooling load in summer, a secondary effect worth noting though rarely dominant). Outputs to track include the cumulative CO₂-equivalent emissions associated with that electricity draw and, for the LED's driver electronics, any electromagnetic interference or power-factor consideration relevant to grid-side impacts, though these are minor next to the direct energy consumption term.

(c) Classification, characterization and evaluation

Working from the use-phase inventory built in (b): Classification sorts each inventory flow into the impact category it contributes to — grid-electricity-generation CO₂ classifies under global warming; upstream criteria-pollutant emissions from fossil-fuel generation (where the grid mix includes them) classify under both acidification and human respiratory health; and the LED's phosphor/semiconductor material inputs classify under resource depletion/rare-material use. Characterization converts each classified flow into a common unit within its category using established equivalency factors — the grid electricity's CO₂ and any associated CH₄/N₂O from upstream generation are summed into a single "kg CO₂-equivalent per 20,000 illumination-hours" score using 100-year global-warming-potential factors. Evaluation (normalization and weighting) then combines the category scores into an overall comparative judgement, e.g. normalizing the global-warming score against a regional per-capita reference load and weighting it against the manufacturing-phase rare-material depletion score established for the LED, so that a single relative ranking of "LED" vs. "incandescent" per 20,000-illumination-hour functional unit can be reported.

Assumptions to state explicitly: the assumed local grid emissions intensity (the single most sensitive parameter in this comparison — a coal-heavy grid widens the LED's advantage far more than a hydro-dominant Canadian grid, where the manufacturing-phase gap narrows the overall margin); the assumed bulb-replacement rate and any incandescent bulb failures before end of rated life; a 100-year global-warming-potential time horizon; and an assumed end-of-life recovery rate for the LED's aluminum heat sink and any rare-earth phosphor content (increasingly addressed by Canadian electronic-waste stewardship programs), which should not be ignored when scoring the LED's end-of-life phase.

(d) Benchmark compounds and their environmental concern