EngiMetric Arena / Interpret & Validate
Does a lower A1-A3 carbon total prove a lower whole-life carbon?
Competency Evidence interpretation primary Quantitative reasoning supporting
What you should take away: Distinguish a cradle-to-gate material comparison from a whole-life carbon assessment and state the scope boundary explicitly.
The situation
What is happening
A screening compares a concrete frame using 100 000 kg of concrete at 0.12 kg CO2e/kg with a steel frame using 10 000 kg of steel at 1.5 kg CO2e/kg. Both factors are labelled A1-A3 only. The concrete option totals 12 t CO2e and the steel option 15 t CO2e. A colleague concludes that the concrete frame has lower whole-life carbon. Choose the defensible interpretation.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Concrete quantity | 100 000 | kg | Concrete frame material. |
| Concrete factor | 0.12 | kg CO2e/kg | A1-A3 only. |
| Steel quantity | 10 000 | kg | Steel frame material. |
| Steel factor | 1.5 | kg CO2e/kg | A1-A3 only. |
| Concrete total | 12 | t CO2e | 100 000 x 0.12 / 1 000. |
| Steel total | 15 | t CO2e | 10 000 x 1.5 / 1 000. |
Assumptions this challenge makes
- Both emission factors are user-supplied and carry an A1-A3 scope label.
- The quantities are compared on the same functional basis.
- Transport, construction, maintenance and end-of-life are not included in either factor.
Your call
Your answer
Hints
- Read the factor scope, not just the total. What lifecycle modules are included?
- A whole-life comparison needs more than material production. Which stages are missing?
- A calculator total is arithmetic on the factors you supplied. Does that verify the factors themselves?
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The engine gives the concrete option 100 000 x 0.12 = 12 000 kg CO2e and the steel option 10 000 x 1.5 = 15 000 kg CO2e.
- The steel option is 3 000 kg CO2e higher, or 25 % above the concrete option.
- Both factors are A1-A3 only. That covers raw-material extraction and production, not transport to site, construction, maintenance, replacement or end-of-life.
- The defensible conclusion is therefore narrower: concrete has the lower A1-A3 material total for these quantities. It is not a whole-life conclusion.
- A whole-life comparison would need a common functional unit, the missing lifecycle modules and factors with declared provenance and geography.
What this challenge does not establish
- The factors are user-supplied and are not verified by the engine.
- The quantities are not converted to a common functional unit beyond the stated comparison.
- The calculation does not include transport, construction, maintenance, replacement or end-of-life.
- A 25 % difference in A1-A3 does not establish a 25 % difference in whole-life carbon.