Question: Why is the method described in this passage not compatible with ISO 14042?

Because the characterisation and weighting steps have been combined.

Because ISO 14042 requires life cycle impact assessment to be scientifically valid, transparent, and based on environmental mechanisms rather than arbitrary value choices.

The method in the passage is not compatible with ISO 14042 if it:

- combines different impact categories into a single score using subjective weighting,
- relies on qualitative or non-scientific ranking instead of characterized impact indicators,
- mixes characterization, normalization, and weighting in a non-transparent way,
- or uses value judgments without clearly separating them from the objective LCIA steps.

In short: it is incompatible because ISO 14042 only allows weighting as an optional, explicitly identified step, and does not accept methods that obscure scientific cause-effect modeling with subjective aggregation.

The context does not state why a specific method is not compatible with ISO 14042. It only says that ISO 14042 provided the methodological framework for impact assessment and that deviations from ISO were introduced only when there were significant arguments for doing so (Guinée et al., Handbook on LCA, 2002, p.526).

Because ISO 14042 provides the methodological framework and proposed issues for impact assessment, and approaches that deviate from those ISO proposals were introduced “only in cases where there are significant arguments for doing so” after further operationalisation. So a method is not compatible with ISO 14042 if it departs from that ISO 14042 framework/proposals rather than following them. (Guinée et al., Handbook on LCA, p.526)

Relatedly, ISO 14042 / ISO 14041 can leave room for “different interpretations” and some procedures “cannot be consistently and unambiguously applied,” which is another reason a described method may not be fully ISO-compatible. (Guinée et al., Handbook on LCA, p.676)


Question: What should be done first if a weighting is performed in a life cycle assessment?

If a weighting is performed, one should first formulate the conclusions that can be drawn without weighting.

Before performing weighting in an LCA, you should first **normalize the impact category results**.

So the usual order is:

1. **Characterization**
2. **Normalization**
3. **Weighting**

Normalization puts the different impact categories on a comparable scale, which is necessary before assigning relative importance through weighting.

If weighting is performed, the environmental impact categories to be covered, the LCIA methods, and the normalisation and weighting sets should be determined prior to the initial inventory analysis, as far as feasible, to avoid interest-driven selection based on initial results.
(Source 1: European Commission – JRC, ILCD Handbook: General Guide for LCA, 2010, p.108)

If weighting is performed, the **environmental impact categories to be covered, the LCIA methods, and the normalisation and weighting sets (if included) should be determined prior to the initial inventory analysis, as far as feasible**. This is to avoid interest-driven selection based on initial results.
**(European Commission – JRC, ILCD Handbook: General Guide for LCA (2010), p.108)**


Question: What model was used to calculate the new toxicity factors in the PhD project at the UVA?

The more recent USES 2.0 model was used to calculate the new toxicity factors.

The new toxicity factors in the UVA PhD project were calculated using the **USEtox** model.

If you want, I can also explain which version and how it is typically applied in LCA toxicity characterization.

The new toxicity factors were calculated using the **USES 2.0 model**.
**Citation:** Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), **p. 9**.

The new toxicity factors were calculated using the **USES 2.0 model**. (Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards*, p. 9)


Question: How is the Environmental Increment factor defined in Solberg-Johansen's method for assessing environmental impacts of radionuclide emissions?

The Environmental Increment factor for radionuclide i in medium j is defined as one standard deviation of the mean background concentration.

In Solberg-Johansen’s method, the **Environmental Increment (EI) factor** expresses the **increase in environmental radioactivity concentration caused by a unit release of a radionuclide**.

In practical terms, it is defined as the **increment in concentration in an environmental compartment** (such as air, water, soil, sediments, or biota) **per unit emission rate or per unit emitted activity** of the radionuclide.

So conceptually:

**EI factor = change in environmental concentration / radionuclide emitted**

It is used as an intermediate fate/exposure factor linking an emission to the resulting contamination level in the environment.

In Solberg-Johansen’s method, the Environmental Increment factor for radionuclide *i* in medium *j* is defined as “one standard deviation of the mean background concentration.”
Source: Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), p.617.

In Solberg-Johansen’s method, the Environmental Increment factor for radionuclide \(i\) in medium \(j\) is defined as “one standard deviation of the mean background concentration.” It appears together with the radionuclide half-life in the effect component of the model. (Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, p.617)


Question: What units should inventory data be expressed in when using characterisation factors for LLW and ILW/HLW?

Inventory data should be in Bq.yr or Bq per nuclide.

When applying characterisation factors for radioactive waste in LCA, the inventory should be expressed in the same waste-category units the factors were derived for:

- **LLW**: use **volume of low-level waste**, typically **m³ LLW**
- **ILW/HLW**: use **mass of intermediate-/high-level waste**, typically **kg ILW/HLW** (sometimes reported as tonnes, but match the factor)

So the key rule is: **express the inventory in the reference unit of the characterisation factor**. For these factors, that is usually **m³ for LLW** and **kg for ILW/HLW**.

The provided context does not state the specific units for inventory data when using characterisation factors for LLW and ILW/HLW.

Relevant general guidance is:
- Inventory data should per default be reported in SI units: ILCD Handbook, p.204.
- For radioactive emissions, activity is expressed in kBq in the example given: Guinée et al. (2002), p.354.
- Preferred units table lists emissions of chemicals, including radioactive isotopes, but the unit is not visible in the provided excerpt: Guinée et al. (2002), p.139.

The context does not state specific units for inventory data “when using characterisation factors for LLW and ILW/HLW.”

What it does state is that:
- “Per default the SI units shall be used for reporting” of inventory data (ILCD Handbook, p.204).
- For emissions of chemicals, the preferred unit for unit-process data collection/reporting is “kg” (Guinée et al., p.139).
- For radioactive emissions, an example uses activity in “kBq,” with characterisation factors combined with emitted activity to calculate indicator results (Guinée et al., p.354).

So from the provided context, no LLW/ILW/HLW-specific unit requirement is given.


Question: What does ISO 14042 state about weighting in the context of comparative assertions disclosed to the public?

According to ISO 14042, weighting is not allowed for comparative assertions disclosed to the public.

ISO 14042 states that **weighting shall not be used in LCA studies intended to support comparative assertions disclosed to the public**.

In other words, if you are publicly comparing products or systems using LCA, you may not apply weighting of impact categories as part of the comparison, because weighting introduces value choices that can affect the outcome.

ISO 14042 states that weighting shall not be used for comparative assertions disclosed to the public. This is stated in Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), p.630, under the heading “weighting,” and also reiterated on p.633.

Citations:
- Guinée et al. (2002), p.630
- Guinée et al. (2002), p.633

ISO 14042 states that **weighting shall not be used for comparative assertions disclosed to the public** (Guinée et al., *Handbook on LCA*, 2002, **p.630**).

This is also reiterated in the recommendations: “according to ISO weighting shall not be used at all for comparative assertions disclosed to the public” (Guinée et al., *Handbook on LCA*, 2002, **p.633**).


Question: What are the two main sides of an Environmental Impact Assessment (EIA)?

An EIA has both a procedural side and an analytical side.

The two main sides of an Environmental Impact Assessment (EIA) are:

1. **The environmental side**
   - Identifies and evaluates how a project may affect the environment
   - Includes impacts on air, water, soil, biodiversity, noise, landscape, and human health

2. **The decision-making / project planning side**
   - Uses the assessment results to support planning and approval decisions
   - Includes comparing alternatives, mitigation measures, and whether the project should proceed

In simple terms: **one side studies the impacts, and the other side uses that information to guide decisions.**

An Environmental Impact Assessment (EIA) has two main sides: a procedural side and an analytical side. Procedural aspects ensure the EIA dovetails with relevant legislation and includes public participation and expert counsel; analytical aspects assess environmental impacts such as risks, land use, waste production, and raw materials and energy consumption. (Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, 2002, p.664)

An Environmental Impact Assessment (EIA) has two main sides: a **procedural side** and an **analytical side**. The procedural side ensures the EIA fits with relevant legislation and includes public participation and expert counsel; the analytical side assesses environmental impacts, including risks and issues such as land use, waste production, and raw materials and energy consumption. (Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), p. 664)


Question: What unit is used to express the Human Toxicity Potential (HTP) characterization factors shown in the table?

The HTP characterization factors are expressed in kg 1,4-DCB equivalents per kg (kg 1,4-DCB eq./kg).

Human Toxicity Potential (HTP) characterization factors are typically expressed in:

**kg 1,4-dichlorobenzene equivalents (kg 1,4-DCB-eq)**

This means the toxicity impact of a substance is normalized relative to **1,4-dichlorobenzene** as the reference substance.

The HTP characterization factors in the table are expressed in **kg 1,4-dichlorobenzene equivalent per kg emission**.
**Citation:** Guinée et al. (2002), Part 2b, p.76.

The Human Toxicity Potential (HTP) characterisation factors in the table are expressed in **kg 1,4-dichlorobenzene equivalent per kg emission** (“**kg 1,4-dichlorobenzene eq/kg emission**”).
Source: **Guinée et al. (2002), Part 2b impact category human toxicity, p. 76**.


Question: What is the preferred time span for fate and effects in life cycle assessment, and what is the secondary option?

The preferred time span for fate and effects is eternity, with 100 years as a second option.

In life cycle assessment, the commonly preferred time span for **fate and effect modelling** is **infinite time horizon** (sometimes described as “until all emissions have exerted their effects”).

The usual **secondary option** is a **100-year time horizon**.

So, in short:

- **Preferred:** **Infinite**
- **Secondary:** **100 years**

The preferred time span is **eternity** for fate and effects; the **secondary option is a long but finite time horizon/integration period chosen by the practitioner depending on the period studied**.

Cited:
- **Guinée et al. (2002), p.595** — “time span … **eternity**”
- **Guinée et al. (2002), p.572** — IPCC GWPs use **20, 100 and 500 years**, and “the integration period … depends on the period over which the impacts are to be studied”

For fate and effects in LCA, the preferred time span is **eternity**; the **secondary option** is a **long but finite time horizon** when an infinite horizon is not applied. This is reflected in the toxicity indicator table listing the time span as **“eternity”** for fate and effects, and in the guidance that a **long horizon would appear to be preferable** for characterisation, though it increases uncertainty.
**Citations:** Guinée et al., *Handbook on LCA*, **p.595**; **p.572**.


Question: How can LCA methodology be applied within an EIA?

Elements of the LCA methodology can be used to run scenario calculations in order to pronounce more reliably on the 'environmental compatibility' of given alternatives.

LCA can complement an Environmental Impact Assessment (EIA) by adding a **life-cycle perspective** to project evaluation.

## How it is applied within an EIA

### 1. Define the project system broadly
In EIA, impacts are often assessed mainly at the project site and during operation. LCA expands this to include:
- **Upstream**: raw material extraction, energy supply, transport, manufacturing of inputs
- **On-site**: construction, operation, maintenance
- **Downstream**: waste treatment, decommissioning, recycling, disposal

This helps avoid shifting impacts from one stage or place to another.

### 2. Support alternatives assessment
LCA can compare project options such as:
- different technologies
- material choices
- energy sources
- construction methods
- waste management options

It provides a structured basis for identifying the option with lower overall environmental burden.

### 3. Quantify indirect and cumulative impacts
EIA typically focuses on direct local impacts. LCA can quantify broader impacts such as:
- climate change
- acidification
- eutrophication
- resource depletion
- human toxicity
- ecotoxicity
- water use

This is useful where indirect supply-chain effects are important.

### 4. Improve mitigation planning
LCA can identify **hotspots** across the life cycle, showing where mitigation will be most effective. For example:
- reducing embodied carbon in materials
- changing fuel or electricity mix
- improving transport logistics
- designing for reuse or recycling

### 5. Inform significance evaluation
LCA results can be used as additional evidence in judging impact significance in EIA, especially for global and regional issues like GHG emissions or resource use.

### 6. Support monitoring and management
LCA can help define environmental performance indicators for follow-up, such as:
- kg CO2e per unit output
- energy demand
- water footprint
- waste generation over the project life

## Typical workflow
- Set **goal and scope** aligned with the EIA decision context
- Define the **functional unit**
- Establish **system boundaries**
- Compile **life-cycle inventory**
- Conduct **impact assessment**
- Interpret results and integrate them into the EIA alternatives, mitigation, and residual impact sections

## Key benefits in EIA
- captures off-site and long-term impacts
- supports more robust comparison of alternatives
- reduces burden shifting
- strengthens transparency and evidence base

## Limitations
- data intensive
- often less site-specific than core EIA studies
- may not capture local ecological or social sensitivities well
- uncertainty can be significant
- should **complement, not replace**, conventional EIA methods

## In practice
LCA is most valuable in EIA for projects with major material, energy, or supply-chain implications, such as:
- infrastructure
- buildings
- energy systems
- waste facilities
- industrial plants

So, within an EIA, LCA is best used as a **decision-support tool** to broaden the assessment from local project impacts to whole-life environmental performance.

LCA can be applied within an EIA as part of the decision-making process, but in the cited source this is described mainly in terms of procedural embedding: LCAs may be performed “as part of Environmental Impact Assessment (EIA) procedures,” even where the broader procedure did not explicitly provide for LCA. The source further notes that relevant process aspects and potential bottlenecks should be considered when embedding LCA in such procedures.

Source: Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), p.432.

The provided context says that LCAs can be performed **as part of Environmental Impact Assessment (EIA) procedures**, though in such cases the broader procedure does **not necessarily explicitly provide for LCA execution**:

> “In other instances, such as **LCAs performed as part of Environmental Impact Assessment (EIA) procedures**, this was not the case.” The text further notes that LCA-based decision-making is often procedurally embedded and discusses relevant process aspects and bottlenecks for such embedding. (Guinée et al., *Handbook on LCA*, p.432)

The context also shows that LCA is one of several environmental tools **used in EIA**, characterized by its **entire life cycle** orientation:

> In Table B1, LCA is listed among tools “**used in EIA**,” with orientation to the chain as “**entire life cycle**.” (Guinée et al., *Handbook on LCA*, p.666)

So, within an EIA, LCA methodology can be applied by carrying out an LCA study as part of the EIA procedure to provide an **entire life-cycle-based environmental analysis** of the project or product system. (Guinée et al., *Handbook on LCA*, pp.432, 666)


Question: What are the two time horizons used for the Human Toxicity Potential (HTP) columns presented in the table?

The two time horizons used for the HTP columns are 500 years (HTP 500 yr) and infinity with continuous emissions (HTP inf-cont).

The two time horizons commonly used for **Human Toxicity Potential (HTP)** in LCA tables are:

- **HTP 100 years**
- **HTP infinite (∞) / long-term**

These represent toxicity impacts evaluated over a **100-year period** and over an **infinite time horizon**, respectively.

The two HTP time horizons used in the table are infinite and 100-year.

Citation: Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), Part 2b: Operational annex 4.3.7 Human toxicity, p.190 (“HTP factors for characterising human toxic releases, for infinite and 100-year time horizons and global scale.”)

The HTP table uses two time horizons: **infinite** and **100-year**. This is stated in **Table 4.3.7.1: “HTP factors for characterising human toxic releases, for infinite and 100-year time horizons and global scale.”**
**Citation:** Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), **Chapter 4.3.7, p.190**.


Question: How is process data typically quantified in existing LCA databases?

In existing LCA databases, process data are almost always quantified in relation to some physical (reference) flow, such as one kg of material or 1 MJ of electricity.

In most existing LCA databases, **process data is quantified as exchanges per functional unit or reference flow**.

Typical features are:

- **Inputs and outputs are listed quantitatively** for a defined process
  - e.g. kg of raw materials
  - MJ or kWh of energy
  - transport in t·km
  - emissions in kg

- The data is usually normalized to:
  - **1 unit of product/service** (the **reference product**), or
  - a specified **functional unit** if used at the process level

- Exchanges are categorized as:
  - **technosphere flows**: materials, fuels, electricity, services from other processes
  - **biosphere/elementary flows**: emissions to air, water, soil, and resource extractions

- Databases often provide:
  - **average**, **site-specific**, or **market** datasets
  - data for a specific **geography**, **time period**, and **technology**

So, in short: **processes in LCA databases are usually represented as unit process inventories, with all material/energy inputs and emissions quantified per reference flow of the process output.**

Process data in existing LCA databases is “almost always quantified in relation to some physical (reference) flow (e.g. one kg of material or 1 MJ of electricity).”
— Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), p.495, Chapter 3.7 “Data collection”

In existing LCA databases, process data is typically quantified “in relation to some physical (reference) flow,” such as “one kg of material or 1 MJ of electricity” (Guinée et al., Handbook on LCA, p.495).


Question: What should category indicators and models include regarding fate, exposure, and effects?

The category indicators and models should include the modeling of fate, exposure, and effects, as relevant.

They should be **scientifically and technically valid**, and include:

- **Fate models**: how emissions move, transform, and persist in the environment.
- **Exposure models**: how humans or ecosystems come into contact with the pollutant.
- **Effect models**: the relationship between exposure and resulting damage or impact.

In LCIA, category indicators and models should therefore be based on accepted environmental mechanisms linking an emission or resource use to its potential impact.

They should include the modeling of fate, exposure, and effects, as relevant, and should include effects below thresholds (“less is better” approach). (Guinée et al., Handbook on LCA, 2002, p.165)

Category indicators and models “should include the modeling of fate, exposure and effects, as relevant,” and they “should include effects below thresholds.” (Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards*, p.165)


Question: What is the purpose of introducing the Simplified LCA level?

The Simplified LCA level was introduced to provide a basis for performing faster and cheaper LCAs than Detailed LCAs.

The **Simplified LCA** level is introduced to make life cycle assessment **more accessible, faster, and less resource-intensive** when a full LCA is not feasible.

Its main purposes are to:

- **Lower the barrier to entry** for organizations with limited data, time, budget, or expertise
- **Support early-stage decision-making** when approximate environmental insights are enough
- **Enable screening and hotspot identification** before investing in a more detailed study
- **Increase uptake of LCA methods** among SMEs, designers, and policymakers
- **Provide proportionate assessment** where the decision context does not require a full ISO-compliant LCA

In short, Simplified LCA helps users get **practical environmental guidance with reduced complexity**, while accepting lower precision than a complete LCA.

The simplified LCA level was introduced “to provide a vehicle for performing faster and cheaper LCAs, which may well be sound enough for certain applications.” (Guinée et al., 2002, p.405)

The simplified LCA level was introduced “to provide a vehicle for performing faster and cheaper LCAs, which may well be sound enough for certain applications” (Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards*, 2002, p. 405).

Relatedly, simplification is defined as reducing LCA complexity “and so reduce the cost, time and effort required to run it” (Guinée et al., 2002, p. 464).


Question: What symbol is used in the table to indicate that a characterization factor value is not available for a given substance?

The symbol 'X' is used to indicate that a characterization factor value is not available.

A dash/hyphen (`-`) is typically used to indicate that a characterization factor value is not available for a given substance.

The symbol is “n/a” (“information was not available or that a property is not applicable”).
Source: Hauschild et al., *LCA: Theory and Practice*, Chapter 40 Annex to Chapter 10, p.1151.

The symbol is **“n/a”**, meaning the information was not available or the property is not applicable. (Hauschild et al., *LCA: Theory and Practice*, Ch. 40, p. 1151)


Question: What is the key distinction between a Detailed LCA and a Simplified LCA in terms of compliance and constraints?

A Detailed LCA complies with ISO standards and is not dominated by time and resource constraints, while a Simplified LCA does not fully comply with ISO standards (e.g., in data collection, data quality requirements, data validation, and allocation) due to time and resource constraints.

The key distinction is:

- **Detailed LCA**: intended to be **fully compliant** with recognized LCA standards/methodological requirements (for example ISO 14040/14044 or product-category rules), with **fewer simplifications allowed** and stricter data, system boundary, and reporting requirements.

- **Simplified LCA**: a **streamlined, less resource-intensive** version that uses **more assumptions, cut-offs, generic data, or reduced scope**, and therefore is **not necessarily fully compliant** with all formal LCA standards or comparative assertion requirements.

In short: **Detailed LCA prioritizes full methodological compliance; Simplified LCA relaxes constraints to save time and effort.**

The key distinction is that a **Detailed LCA** is based on practical guidelines **complying with ISO standards**, where **time and resource constraints do not play a dominant role**, whereas a **Simplified LCA** is based on practical guidelines **not fully complying with ISO standards**—for example on data collection, data quality, validation, and allocation—**because of time and resource constraints**, in order to enable faster and cheaper studies.
**Source: Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), p.465**

The key distinction is:

- **Detailed LCA**: “an LCA based on practical guidelines **complying with ISO standards**, where **time and resource constraints do not play a dominant role**” (Guinée et al., *Handbook on LCA*, **p. 465**).
- **Simplified LCA**: “an LCA based on practical guidelines **not fully complying with ISO standards** … for reasons associated with **time and resource constraints**; the simplified level has been introduced to provide a basis for performing **faster and cheaper** LCAs than detailed LCAs” (Guinée et al., *Handbook on LCA*, **p. 465**).

This is also echoed on **p. 405**, where Guinée et al. state that guidelines for simplified LCA are “largely in line with the ISO standards, **but not entirely**,” while detailed LCA guidelines “**comply fully** with the various ISO Standards” (Guinée et al., *Handbook on LCA*, **p. 405**).


Question: What unit is used to express both the MAETP (inf) and FSETP (inf) characterization factors listed in the table?

Both MAETP (inf) and FSETP (inf) characterization factors are expressed in kg 1,4DCB eq./kg.

Both **MAETP (inf)** and **FSETP (inf)** characterization factors are typically expressed in:

**kg 1,4-DCB-eq**

That means **kilograms of 1,4-dichlorobenzene equivalent**.

Both MAETP (inf) and FSETP (inf) are expressed in **kg 1,4-DCB eq./kg**.
Source: Guinée et al. (2002), **p.240**.

Both **MAETP (inf)** and **FSETP (inf)** are expressed in **kg 1,4-DCB eq./kg** (or **kg 1,4DCB eq./kg**).
Cited in the table on **Chapter 4, p.243** of Guinée et al. (2002).


Question: What is the difference between how LCA databases and companies typically organise process data in terms of time?

LCA databases organise process data around unit processes relating outputs to inputs without a time dimension, whereas companies often provide process data in terms of inputs and outputs per unit of time, such as emissions or material inputs per year.

In short:

- **LCA databases** usually organize process data as **time-averaged, static datasets**. A process represents a “typical” technology, geography, and period (for example, “EU electricity mix, 2020” or “average steel production, 2018–2022”). Time is often implicit and coarse.
- **Companies** usually organize process data as **operational, time-stamped records**. Their data are tied to specific periods such as batches, shifts, days, months, or fiscal years, because they collect data for accounting, control, and reporting.

So the main difference is:

1. **Granularity**
   - Databases: aggregated over a representative time period.
   - Companies: often fine-grained and chronological.

2. **Purpose**
   - Databases: comparability and reuse in LCA modeling.
   - Companies: operational management, compliance, cost tracking, ERP/MES reporting.

3. **Temporal behavior**
   - Databases: mostly static snapshots.
   - Companies: dynamic, reflecting seasonality, downtime, supplier changes, and process improvements over time.

4. **Modeling implication**
   - In LCA databases, time is usually simplified away.
   - In company data, you often need to aggregate or harmonize time series before using them in an LCA.

So, LCA databases tend to store **representative process datasets**, while companies tend to store **time-resolved process records**.

LCA databases almost always quantify process data relative to a physical reference flow, such as 1 kg of material or 1 MJ of electricity, whereas companies often organise process data per unit of time, such as tonnes per year of emissions or inputs.

(Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, 2002, p. 51)

LCA databases usually quantify process data relative to a physical reference flow, such as “1 kg of material” or “1 MJ of electricity,” whereas companies often organise process data per unit of time, e.g. “5 tonnes per year” emitted or “1000 tonnes of wood per year” consumed (Guinée et al., Handbook on LCA, p.51).


Question: Under what condition might two technically separable linked functions still not be regarded as comparable to their joint functions?

When, due to other aspects beyond technical possibility, the two separate functions may still not be regarded as comparable to the joint functions.

In LCA, even if two linked functions are technically separable, they may still **not be considered comparable to the joint functions** when **the determinants causing the linkage are relevant to the decision context or to the studied system’s behavior**.

A common case is when the linked outputs are **economically or physically interdependent**, so separating them would misrepresent how the system actually responds to changes in demand.

So, the key condition is:

**If separating the functions would ignore relevant causal relationships or constraints that make the co-production meaningful in the assessed context, the separable functions should not be treated as comparable substitutes for the joint functions.**

Two technically separable linked functions may still not be regarded as comparable to their joint functions “due to other aspects,” even if technical separation is possible.

Chapter/page: Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards (2002), p.469.

Two technically separable linked functions may still not be regarded as comparable to their joint functions “due to other aspects,” even when technical separation is possible. (Guinée et al., Handbook on LCA, p.469)


Question: What assumption is made about crude oil input when the composition of independently variable economic outputs changes?

The same amount of crude oil input is assumed irrespective of the relative composition of the independently variable economic outputs.

The usual assumption is that **the crude oil input mix stays fixed/proportional** even if the composition of the independently variable economic outputs changes.

In other words, changing the output composition is assumed **not to alter the type or amount of crude oil required per unit of activity**, unless a specific model adjustment is made.

The assumption is that the **same amount of crude oil input is used irrespective of the relative composition of the independently variable economic outputs**.

**Source:** Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), **Part 2b: Operational annex, p.156**.

The assumption is that **the same amount of crude oil input is used irrespective of the relative composition of the independently variable economic outputs**.
(Guinée et al., *Handbook on LCA: Operational Guide to the ISO Standards* (2002), Part 2b: Operational annex, p.156)


Question: Under what condition will combustion emissions increase in a refinery when independently variable economic outputs change?

Combustion emissions will increase if additional processing is needed to produce more of a fraction than the result of one crude distillation and one cracking of the distillation residue.

Combustion emissions in a refinery will increase when the change in independently variable economic outputs causes the refinery to require more fuel combustion for process energy.

In practical LCA/refinery terms, this happens when:

- the output mix shifts toward more energy-intensive products or processes, or
- total throughput rises in a way that increases fired heating, steam, hydrogen production, or utility demand.

More formally, emissions increase if the net change in product outputs leads to a positive increase in total refinery energy demand, given the refinery’s marginal energy/emissions relationships.

So the condition is:

> combustion emissions increase when the independently varied outputs produce a positive marginal increase in refinery combustion energy use.

Combustion emissions will increase when additional processing is needed to produce more of a fraction than results from one crude distillation and one cracking of the distillation residue; this processing requirement depends on the composition of the raw material input. (Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, 2002, Part 2b: Operational annex, p.156)

Combustion emissions will increase “if additional processing is needed to produce more of a fraction than the result of one crude distillation and one cracking of the distillation residue.” The text adds that “the processing requirement depends on the composition of the raw material input.” (Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, 2002, chapter 3.9.3.2, p.156)


Question: What is an example of two functions so intimately linked that their separation is not possible?

The heat generation of a light bulb cannot be detached from its primary function of lighting.

A classic LCA example is **raising sheep for both wool and meat**.

These two functions are often considered **intimately linked** because the same biological system produces both outputs together, and separating the process into independent wool-production and meat-production functions is not realistically possible.

Another common example is **dairy cows producing both milk and calves/meat**.

An example is “the heat generation of a light bulb” and its primary function “lighting”; their separation is not possible.
(Guinée et al., Handbook on LCA, p.469)

An example given is **a light bulb’s heat generation and its primary function of lighting**: “the heat generation of a light bulb cannot be detached from its primary function lighting” (**Guinée et al., Handbook on LCA: Operational Guide to the ISO Standards, p. 469**).