VOICE-OVER: Welcome to the tutorial...
for using ConsExpo Web's vapour release modes...
to estimate the inhalation of vapours released in consumer exposure scenarios.
The tutorial includes an introduction to the instantaneous release...
constant rate and evaporation modes...
and content about the input fields that are specific to these modes.
In this introduction, we briefly explain the vapour modes...
included in ConsExpo Web...
so that you are able to select the mode that is appropriate...
for your specific consumer exposure scenario.
ConsExpo Web includes vapour exposure scenarios...
in which the consumer uses a liquid product...
from which volatile substances evaporate into the room.
Examples of such products are paints, cleaning products...
and liquid air fresheners.
All of ConsExpo Web's vapour modes...
require the user to enter a value for exposure duration, room volume...
ventilation rate and inhalation rate...
and provide the option to enter a value for absorption...
to assess internal inhalation exposure.
This applies to all inhalation modes...
and is therefore explained in the introduction...
to the inhalation modes tutorial.
The instantaneous release mode is the simples vapour mode...
included in ConsExpo Web.
It simply assumes that all of the substance is released into the room at once.
Note that the concentration in the air immediately reaches its peak...
as the substance is released immediately.
As such, the instantaneous release mode...
also delivers the highest simulated exposure dose.
This mode is most suitable for cases for which limited data are available...
or when the user wants to obtain a conservative estimate...
of inhalation exposure.
The constant rate mode assumes that the substance is gradually released over time.
The concentration in the air increases...
as the substance evaporates at a constant rate over time.
The release stops once the substance is depleted...
as in the case, for example, of a long-lasting air freshener...
or when the emission source is removed...
for example when a bucket of cleaning product is flushed down the drain...
or when a bottle is closed.
The evaporation mode is ConsExpo Web's most complex vapour mode.
It simulates the evaporation of a substance from a product or treated surface...
based on its vapour pressure, molecular weight...
and the properties of the liquid product matrix containing the substance.
This mode is more precise than the instantaneous release...
and constant rate modes...
but also requires a higher level of detail in the input fields.
We will now explain the inputs that are required...
specifically for the instantaneous release and constant rate release modes.
Both release modes require the user to enter a product amount...
which refers to the amount of liquid product used in the consumer exposure scenario...
expressed as a unit of mass, such as grams or milligrams.
The constant rate release mode also requires the user...
to enter the emission duration.
This duration refers to the time during which the substance is released into the room.
In a consumer exposure scenario...
this may be the time between the moment a product is applied to a surface...
and the moment it is wiped off that surface...
the time between the moment a product is poured into a container...
and the moment it is flushed down the drain...
or the time during which a container holding a liquid product is left opened.
The emission duration is expressed as a unit of time...
such as minutes, hours or days.
Both the instantaneous and the constant rate release modes...
provide the option to limit the air concentration...
to the saturated vapour pressure.
When choosing this option, ConsExpo Web simulates a balance...
between the concentration of the substance in the air...
and the amount of the substance deposited onto the walls, floor or furniture...
as displayed here in the animation...
of cleaning a floor with a cleaning product and a mop.
In order to calculate this balance...
ConsExpo Web requires the user to enter values...
for the vapour pressure and molecular weight of the substance...
as well as the temperature at which the product is applied.
Usually, this application temperature is the room temperature...
which is set to 20 degrees Celsius by default.
Please note that the balance between the concentration of the substance in the air...
and the amount of the substance...
is maintained during the release of the substance from the product...
and throughout the reduction of the concentration in the air due to ventilation.
The consequence of including the option to limit the air concentration...
to the saturated vapour pressure...
is that the peak of the concentration in the air is lower...
but the reduced concentration may persist over a longer period of time.
The upcoming graphs display typical simulations of an instantaneous release...
constant rate release...
and constant rate release with the saturated vapour pressure option selected.
The concentration in the air at instantaneous release...
immediately reaches its peak and then declines due to ventilation.
At constant rate release...
the concentration in the air increases until a maximum is reached...
and then declines due to ventilation.
When the saturated vapour pressure is provided as an input...
the peak reached is lower...
because the substance is also deposited onto the furniture, walls and floor.
However, the concentration of the substance in the air remains stable...
for a longer period of time...
because substance still evaporates from the furniture, walls and floor...
to maintaining the balance with the concentration in the air.
In this next part of the tutorial, we will introduce you to the evaporation mode...
which is the most complex vapour mode included in ConsExpo Web.
This mode requires the user to provide input...
on the chemical properties of the evaluated substance...
such as vapour pressure, molecular weight...
and whether the liquid product is made of 'pure substance'...
which means that the liquid consists of a single substance only.
If, however, the substance is mixed into a liquid with other ingredients...
the evaporation mode also requires input on the chemical properties of that mixture...
such as the molecular weight matrix...
and whether the product is diluted before the consumer uses it.
Liquid cleaning products, for example...
are diluted in a bucket of water before they are used to clean surfaces.
For example, if a product consists of 100% ethanol...
you can select the substance in pure form.
A vapour pressure of 5,950 Pa and a molecular weight of 46 g/mol...
can be entered into the appropriate input fields.
The ConsExpo Web evaporation mode...
is then able to simulate an evaporation rate based on these two chemical properties.
Note that a value of 1 as fraction or 100% as percentage...
needs to be entered into the input field 'Weight fraction substance'.
If, however, the evaluated substance is mixed into a liquid...
that contains other ingredients...
ConsExpo Web needs more information to perform a simulation.
The evaporation rate is derived from the partial vapour pressure of the substance...
within the product matrix, which is based on Raoult's law.
Raoult's law states that the partial pressure...
of each component of an ideal mixture of liquids...
is equal to the vapour pressure of the pure component, liquid or solid...
multiplied by its molecular fraction in the mixture.
In other words, the partial vapour pressure in a substance...
in a liquid consumer product...
is estimated by multiplying the molecular fraction of the substance in the product...
by its vapour pressure.
The molecular fraction is the amount of moles of the evaluated substance...
divided by the total amount of moles in the mixture.
ConsExpo Web includes an input field called 'Molecular weight matrix'...
for simulations that are based on Raoult's law.
Here is a brief example to explain how to enter the appropriate value...
for the molecular weight matrix.
The liquid product in the example is an ideal mixture...
that consists of 75% water, 15% methanol and 10% ethanol.
Note that these are weight fractions.
Ethanol is the substance to be evaluated.
You need to obtain the molecular weights of the other ingredients...
and derive their respective amounts in mole per gram of liquid product...
which you can calculate by dividing the weight fraction of the ingredient...
by its molecular weight.
The evaluated substance, in this example ethanol...
is considered to be separate from the molecular matrix into which it is mixed.
The information on ethanol is therefore crossed out.
The molecular weight matrix is then calculated by dividing the number 1...
by the sum of the amounts in mole per gram of product of the other ingredients.
In this example, the molecular weight matrix is 21.6 g/mol.
In practice, however, the entire composition of the liquid product is often unknown.
In this example, the mixture consists of 70% water and 5% unknown ingredients.
Despite this lack of data, you can still enter a value for the molecular weight matrix.
The molecular weight matrix is then calculated...
using the molecular weights and mass fractions of the ingredients that are known.
In this example, the molecular weight matrix is at most 22.9 g/mol...
as the inclusion of any other ingredient would lower the calculated value.
ConsExpo Web's simulated concentrations in the air...
increase when the molecular weight matrix is increased...
so an estimate of the molecular weight matrix value with missing ingredients...
is a conservative approach.
Note that the molecular weight matrix...
does not include the evaluated substance itself.
If, for example, the substance of methanol is evaluated instead of ethanol...
the value of the molecular weight matrix based on other ingredients...
would be 24.4 g/mol.
In some scenarios, the product is diluted before use.
Common examples are surface cleaning products diluted in a bucket of water...
before the consumer starts to treat surfaces...
or a dishwashing detergent that is diluted in the hot water of a sink or bowl.
In these cases, the evaporation rate is affected by the dilution...
as the product containing the evaluated substance is a mixture as well.
Here, we briefly explain how to enter the appropriate value...
for the number of times the product is diluted.
The number of times a product is diluted...
is derived by dividing the weight of the product used...
by the weight of the overall mixture.
Products are most often diluted in water...
which has a density of 1 milligram per millilitre.
If 10 g of product is diluted in 200 ml of water...
the resulting overall mixture weighs 210 g.
The number of times the product is diluted...
is the sum of the product and solvent amount...
in this case 200 g plus 10 g...
divided by the product amount, in this case 10 g.
In this example, the product is diluted 21 times.
Evaporation is determined by the difference...
between the vapour pressure in the air...
and the saturated vapour pressure of the substance in the product.
The rate of evaporation is proportional to this pressure difference...
and depends on the surface area of the product and the mass transfer coefficient.
This mass transfer coefficient is a measure of how slowly or quickly...
the evaporated substance is transferred from the product surface into the air.
The mass transfer coefficient accounts for the fact...
that emission from a product is limited...
due to the presence of a stagnant layer of air over the product surface...
through which the substance must diffuse to reach the air in the room.
The mass transfer coefficient depends on a number of factors...
such as the substance’s molecular weight, the air flow over the product...
and the surface roughness of the product.
The most recent ConsExpo Web fact sheets suggest a default value...
for the mass transfer coefficient of 10 meters per hour.
Options to calculate a mass transfer coefficient...
using the Langmuir and Thibodeaux methods...
are mentioned in earlier fact sheets, but are considered less appropriate.
The methods are still available in ConsExpo Web as legacy features...
mainly for the purpose of re-evaluating consumer exposure simulations...
performed in the past.
The evaporation mode gives the option...
to simulate the release of a vapour from a ‘constant release area’...
meaning that the area from which the substance evaporates...
does not change over time.
Examples of constant release areas include an opened bottle...
a carpet with stains or kitchen sinks.
Appropriate values for such release areas...
are presented in ConsExpo Web fact sheets.
The emission duration refers to the time...
during which the substance may evaporate from the release area.
For example, a carpet stain treated with a cleaning product is left to soak...
before it is wiped clean.
In that case, the emission duration refers to the soaking period.
Other examples of emission duration...
include the time between the moment at which a product is mixed into a bucket...
and the moment the bucket is flushed down the drain...
or the time between the moment the lid of a paint bucket is removed...
and the moment it is replaced.
The evaporation mode also gives the option to simulate release...
from a release area that increases in size over time...
or an ‘increasing release area’.
Increasing release areas are relevant in scenarios...
in which the product is applied onto a surface that increases in size over time.
ConsExpo Web then corrects for the fact that the release area is not as large...
at the beginning of the consumer exposure as at the end.
Typical examples of exposure scenarios that involve an increasing release area...
include painting a wall or mopping a floor with a cleaning product.
The application duration refers to the time it takes for the consumer...
to apply the product onto such a surface area.
For example, ConsExpo Web fact sheets indicate that it takes 20 minutes...
to treat a surface area of 22 m².
The application duration is therefore 20 minutes.
Here you can see the effect of an increasing or constant release...
on the concentration in the air over time.
In scenarios with an increasing release area...
the concentration in the air gradually increases...
as more product is being applied onto the surface...
from which a substance evaporates.
The concentration in the air still increases after the application duration ends.
Here, the substance still evaporates from the release area...
while ventilation removes the substance released earlier from the air.
In the case of a constant release area...
the concentration in the air increases until the moment emission stops...
and ventilation removes the remaining substance from the air.
In summary, we have used this tutorial to demonstrate...
how to select the appropriate vapour mode that fits your consumer exposure scenario...
and how to make sure to check the appropriate boxes...
and insert appropriate values into the input fields...
that are specific to the instantaneous release...
constant rate or evaporation modes.
We hope that this tutorial has been helpful.
In a later tutorial, we will tell you more about the evaporation mode.
We would like to acknowledge all partners in the ConsExpo project.
Health Canada...
the French Agency for Food, Environmental and Occupational Health & Safety...
the German Federal Institute for Risk Assessment...
the Swiss Federal Office of Public Health...
the Netherlands Food and Consumer Product Safety Authority...
and the Dutch Ministry of Health, Welfare and Sport.