Explanation of BU-AC ralating to evaporation 1

[RLJ]

I am reviewing a MSDS of a product that shows the evaporation rate as:

{Evaporation rate (BU-AC=1) = 0.03}

This is similar to vapor density using air as 1. However, I do not know what BU-AC is or its evaporation rate. Can anyone explain this?

Thanks in advance, RLJ s-)

 

[phoward]

Evaporation Rate

One general reference material for evaporation rates is n-butyl acetate (commonly abbreviated BuAc). Whenever a relative evaporation rate is given, the reference material must be stated.

Taking the relative evaporation rate of butyl acetate as 1.0. Other materials are then classified as:

Speed Evaporation Rate
(BuAc = 1.0) Examples
Fast > 3.0 Methyl Ethyl Ketone = 3.8
Acetone = 5.6
Hexane = 8.3.
Medium 0.8 to 3.0 95% Ethyl Alcohol = 1.4
Naphtha = 1.4
Slow < 0.8 Xylene = 0.6
Isobutyl Alcohol = 0.6
Water = 0.3
Mineral Spirits = 0.1

We are not aware of a specific number for the absolute evaporation rate (i.e. in mass/time units) of butyl acetate. Presumably, such a number would depend on dozens of variables such as temperature, atmospheric pressure, humidity, air flow etc., making it a rather useless information. In the absence of evaporation rate data, you can roughly assess the volatility using the vapor pressure of the material.

Definition
MSDS sheets: An evaporation rate is the rate at which a material will vaporize (evaporate, change from liquid to vapor) compared to the rate of vaporization of a specific known material. This quantity is a ratio, therefore it is unitless.

General usage: The mass of material that evaporates from a surface per unit time (examples: 3 grams per square meter per hour, 1 inch per acre per month).

MSDS Relevance
Evaporation rate can be useful in evaluating the health and fire hazards of a material. For example, a substance with a high evaporation rate will readily form a vapor which can be inhaled or explode.

Evaporation rates generally have an inverse relationship to boiling points; i.e. the higher the boiling point, the lower the rate of evaporation.

 

[RLJ]

phoward,

Excellent batch of information. Additional information: The Boiling point is 350F to 415F; the falsh point is 145F; and the vapor density is 5.3 (air = 1.0).

This, combined with your information, tells me that we should have a very slow evaporating product that will drop and fill low areas (trenches and such).

This should help greatly in finishing the design and improving our confidence level with fume collection and flashpoint issues.
RLJ s-)