CHAPTER 5

FIRE SAFETY

6.0 FLAMMABLE LIQUIDS

 

6.1  Characteristics

6.2  Definitions

6.3  Solvents

6.4  Storage

6.5  Common Safety Problems

6.6  Common Control Measures


6.1       Characteristics

Flammable liquids are volatile in nature; that is, they evaporate quickly, emitting vapors. These vapors readily ignite.

Most vapors:

         are invisible,

         are heavier than air,

         tend to settle to the lowest level possible,

         are difficult to detect.

Vapors may flow down elevator shafts or through air ducts to lower floors and create a fire hazard in an area away from the point of origin.

Although flammable liquids continuously emit vapors, the vapors develop more rapidly in a warm atmosphere or when liquids are near a heat source.  When the vapors ignite, the temperature of the liquid rises.  More vapors are released and the fire burns more fiercely.

 

6.2       Definitions

Flammable liquids vary in the degree of fire and explosion hazard they present.  The degree of hazard depends on two variables the explosive range and the flash point.

         Explosive Range - the range of vapor concentration from the point below which there are not enough vapors combining with the air to ignite, to the point above which the vapor concentration in the air is too great to ignite. 

         Flash Point the lowest temperature of the liquid at which sufficient vapors are emitted to create a flammable mixture of vapor and air.  The lowest temperature at which these vapors are given off rapidly enough to support continuous combustion is the fire point.  This is usually a few degrees above the flash point.

 

6.3       Solvents

Flammable and combustible solvents are divided into six categories (see chart). 

         A flammable liquid is one having a flash point below 100 F (37.8 C) and having a vapor pressure not exceeding 40 psi (absolute) at 100 F (37.8 C).  Flammable liquids are known as Class I Liquids. 

         A combustible liquid is one that has a flash point at or above 100 F (37.8 C).  Combustible liquids are known as Class II or Class III liquids.

Category

Flash Point

       F                    C 

Boiling Point

      F                     C

 

Class IA

Below

73                   22.8

Below

100                 37.8

 

Class IB

Below

73                   22.8

Below

100                 37.8

 

Class IC

at or above

73                   22.8

below

100                 37.8

 

Class II

at or above

100                 37.8

below

140                   60

 

Class IIIA

at or above

140                    60

below

200                 93.3

 

Class IIIB

at or above

200                 93.3

 

                                          

 

6.4       Storage

The amount of flammable solvent that can be stored in any one laboratory depends on the total amount in the overall laboratory unit.  Contact HSS at ext. 21781  for details.  Also refer to Chapter 8, Chemical Safety, concerning the storage of chemicals.

         maintain records, drawings, and maintenance manuals on all fire protection systems on campus.

         obtain welding and cutting permits as required (requirements will be covered later in this chapter).

 

6.5       Common Safety Problems

Avoid:

         Improperly stored glass containers of flammable solvents;

         pouring flammable liquids from metal containers with inadequate grounding (this prevents static sparks generated by flowing liquids);

         mixed solvents in a water disposal can;

         storing solvents (such as ether) in refrigerators that are not explosion-proof;

         fire extinguishers or automatic extinguisher systems that are not explosion proof;

         storing flammable solvents with oxidizer or other reactive chemicals.

 

In laboratories using flammable solvents, make sure that the work area has:

         provisions for solvent spill cleanup, safety showers and fire extinguishers.

 

6.6       Common Control Measures

         Isolate solvents from reactive chemicals.

         Use open containers of solvents only in a properly functioning fume hood.

         Eliminate all sources of ignition.

         Store solvents in a cool area (an area with a maximum temperature of  80 F  (26.7 C).

         Transport solvents and store in metal or other protective containers (safety cans).

         Be thoroughly acquainted with the hazards of flammable solvents.

         Know the location of fire-fighting equipment and how to use it.

         Never store more than a total of five gallons of different types of solvents in a laboratory except in a flammable liquid storage cabinet.

         Make sure drums are grounded to earth and that a bonding wire is used to connect the metals of the drum to the receiving container.  This lessens the chance of static discharge.