I believe most of us would agree that most laboratories use flammable and hazardous chemicals. Recent statistics have shown that chemical spills and fires are two of the most common accidents occurring in labs. Unfortunately, even “small” fires can cause significant damage and serious disruption, not only in the immediate lab where the incident occurred, but also in adjoining labs. Large fires can be devastating, destroying the source lab and sometimes entire buildings.
Flammable solvents can easily catch fire and burn. This article will focus on the proper handling and storage of liquids because, according to Prudent Practices, the most common fire hazard in the typical research lab is a flammable liquid or the vapor produced by one.1
The use of approved safety storage cabinets decreases the risk of devastating chemical fires. Approved safety cabinets must pass a standard 10-minute fire test in which the internal temperature remains below 325 °F (163 °C) despite the heat of the fire. Well-designed safety cabinets help with organizing and storing incompatible chemicals, greatly reducing the chance of unwanted contact and reactions.
The basic “fire triangle” stipulates three conditions that must exist simultaneously for a fire to occur: an oxidizing atmosphere, usually air; a source of ignition; and a concentration of flammable gas or vapor within its flammability limits. If any one of these is removed, a fire cannot occur. Since air is always present, eliminating flammable vapors and gases and controlling potential ignition sources are essential to the prevention of fire hazards.
Physical properties of flammable and combustible substances
There are differences between flammable and combustible materials. Flammable liquids are more dangerous. The distinction is based on flash points, with the flammable class having a flash point below 100 °F (37.8 °C) and combustible liquids having flash points between 100 °F and 200 °F (93 °C). Flash point is the lowest temperature at which there will be enough flammable vapor to ignite when an ignition source is applied. A closely related term is vapor pressure. Every liquid has a vapor pressure, which is a function of the liquid’s temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of flammable liquid vapor in the air increases. Therefore, temperature determines the concentration of vapor of the flammable liquid in the air, and the specific concentration of vapor in the air that is necessary to sustain combustion is the flash point for that flammable liquid.
Another important concept is the flammable range, the range between the upper and lower flammable limits. Flammable limits are expressed in percent volume in air. Concentrations above the upper flammable limit are too rich to burn (too much vapor), and concentrations below the lower flammable limit are too lean to burn (not enough vapors). The most dangerous materials are those with the lowest flash point and the widest flammable ranges.
The National Fire Protection Association’s (NFPA’s) Code for Flammable and Combustible Liquids, NFPA 30, is an excellent resource and introduction to the hazards of these materials.2 NFPA 30 classifies flammables as Class I and divides them into Class IA, IB, and IC, while combustible materials are classified as Class II, Class IIIA, and Class IIIB, all based on flash points and boiling points. NFPA 30 also rates the fire hazard of flammable and combustible materials on a scale of 0 to 4 based on flash point. This rating helps you quickly assess the potential danger of a substance. Zero is the least hazardous and indicates the material will not burn. A rating of 1 is given to materials with flash points above 200 °F and indicates that the material needs to be preheated to burn, while flammables with flash points below 73 °F are rated 4 and are extremely flammable and the most dangerous.
Important criteria for flammable and combustible materials storage
Design and build quality are paramount in selecting a good safety storage cabinet. We recommend looking for double-walled steel cabinets with an insulating space in the doors, sides, top, and bottom. Look for welded or riveted joints and construction for superior strength. Additional design details to look for include a raised door sill of at least two inches at the bottom to contain any spills and secure multi-point door latching.
Although NFPA 30 does not require venting, most safety cabinets will provide this option. Make sure flame arrestors are built in and caps or bungs are supplied to seal the vent if your situation does not call for venting. Another non-mandatory option to consider is grounding. Most well-designed safety cabinets will include a grounding lug. This is recommended to reduce the risk of static spark discharge and is most important for collection or dispensing operations. So, if you anticipate pumping out of a container or pouring into a drum funnel, make sure the cabinet is connected to an earth ground.
Optional adapter bracket kits are a good choice if you are located in an area prone to seismic or hurricane activity. This secures the safety cabinet to a wall or floor and prevents spills from chemicals falling or tipping over.
A few words on quantities of stored hazardous materials
One frequently cited issue is having excessive flammable solvents in the lab. NFPA 45, Fire Protection for Laboratories Using Chemicals, provides universal guidelines for safe storage3, addressing the maximum quantity of flammable and combustible materials stored in labs. Chapter 4 of NFPA 45 classifies laboratories into four fire hazard categories based on the amount of flammable and combustible material in the lab. These are Class A (high fire hazard), Class B (moderate), Class C (low), and Class D (minimal). Class A labs are allowed up to 10 gallons (38 L) of Class I flammable liquid per 100 square feet or 20 gallons (76 L) total of Class I, II, and III flammable and combustible liquid combined. These quantities can be doubled to 20 gallons of Class I liquid and 40 gallons (150 L) of Class I, II, and III liquids combined with the use of safety cans or storage cabinets.
NFPA 45 also recommends maximum capacities for different storage container types. For example, for Class IA flammable liquids, the largest allowed container is one pint (500 mL) for glass, one gallon (4 L) for metal and approved plastic or polyethylene, and 2.6 gallons (10 L) for safety cans. Storing flammable and combustible liquids in laboratories or stockrooms is risky business. Paying attention to the hazard class of the material, the largest container size, and the total quantities will minimize that risk.
1. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. National Research Council. National Academy Press. Washington, D.C. Latest edition.
2. NFPA 30 Flammable and Combustible Liquids Code. 2008 edition. National Fire Protection Association, Quincy, MA. http://www.nfpa.org/aboutthecodes/aboutthecodes.asp?docnum=30&cookie_test=1
3. NFPA 45 Fire Protection for Laboratories Using Chemicals. 2004 edition. National Fire Protection Association, Quincy, MA. http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=45