What is an oxidizer? It can be a solid or a liquid. It yields oxygen or other oxidizing gas and can react to promote or initiate combustion of combustible materials. Under some circumstances, it can undergo a vigorous self-sustained decomposition due to contamination or heat exposure.
Why are oxidizers hazardous? A strong oxidizer can cause explosions and pose fire hazards if they come into contact with certain materials. An oxidizing gas can support and accelerate combustion of other materials.
There are Four Classes of Oxidizers
Class 4 – An oxidizer that can undergo an explosive reaction due to contamination or exposure to thermal or physical shock and that causes a severe increase in the burning rate of combustible materials with which it comes into contact.
Class 3 – An oxidizer that causes a severe increase in the burning rate of combustible materials with which it comes into contact or a solid oxidizer classified as Class 3.
Class 2 – An oxidizer that causes a moderate increase in the burning rate of combustible materials with which it comes into contact or a solid oxidizer classified as Class 2.
Class 1 – An oxidizer that does not moderately increase the burning rate of combustible materials with which it comes into contact or a solid oxidizer classified as Class 1.
Chapter 5 of NFPA 400, Hazardous Material Code includes the Maximum Allowable Quantity (MAQ) of each oxidizer class per Control Area. There are also MAQ’s provided per occupancy. There are tables / exceptions / allowances listed here that are similar to those for combustible/flammable liquids in NFPA 30, Flammable and Combustible Liquids Code. MAQ’s are doubled when automatic sprinklers are provided in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems and if approved cabinets or detached/cutoff rooms are used for such storage. All occupancies shall be permitted to have more than one control area.
A control area is a building or portion of a building or outdoor area, within which hazardous materials are allowed to be stored, dispensed, used, or handled in quantities not exceeding the MAQ.
Please see the NFPA table listed below and the footnotes that apply:
MAQ of Hazardous Materials (Oxidizers) Per Control Area
Storage Solid (lb.) | Storage Liquid (gal.) | Closed System Solid (lb.) | Closed System Liquid (gal.) | Open System Solid (lb.) | Open System Liquid (gal.) | |
Class 4 | 1 c,i | 1 c,i | _ i | _ i | _ i | _ i |
Class 3 | 10 c,d | 10 c,d | 2 d | 2 d | 2 d | 2 d |
Class 2 | 250 c,d | 250 c,d | 250 d | 250 d | 50 d | 50 d |
Class 1 | 4,000 c,e | 4,000 c,e | 4,000 e | 4,000 e | 1,000 e | 1,000 e |
c. Quantities are permitted to be increased 100% where stored or used in approved cabinets, gas cabinets, exhausted enclosures, gas rooms, explosive magazines, or safety cans as appropriate for the material being stored in accordance with NFPA 400. Where footnote d also applies, the increase for both footnote c and footnote d is permitted to be applied accumulatively.
d. Maximum quantities can be increased 100% in buildings equipped with a sprinkler system in accordance with NFPA 13. Where footnote c also applies, the increase for footnote c and footnote d is permitted to be applied accumulatively.
e. The permitted quantities are not limited in a building equipped throughout with an automatic sprinkler system in accordance with NFPA 13.
i. Permitted only in buildings equipped with a sprinkler system in accordance with NFPA 13.
Where quantities of hazardous materials are increased in accordance with Chapter 5 of NFPA 400, such materials shall be stored in accordance with the following limitations:
- Storage and display of solids shall not exceed 200 lb. /ft2 of floor area actually occupied by solid merchandise.
- Storage and display of liquids shall not exceed 20 gal. /ft2 of floor area actually occupied by liquid merchandise.
- Storage and display height shall not exceed 6 ft. above the finished floor.
- Individual containers less than 5 gal. or less than 25 lb. shall be stored or displayed on pallets, racks, or shelves.
- Racks and shelves used for storage or display shall be in accordance with Chapter 6 of NFPA 400.
- Containers shall be listed or approved for the intended use.
- Individual containers shall not exceed 100 lb. capacity for solids or a 10 gal. capacity for liquids.
- Incompatible materials shall be separated in accordance with Chapter 6 of NFPA 400.
- Except for surfacing, floors shall be of noncombustible construction.
- Aisles 4 ft. in width shall be maintained on three sides of the storage or display area.
- Hazard identification signs shall be provided in accordance with Chapter 6 of NFPA 400.
- Oxidizers should be separated from sources of heat such as heating units, piping or ducts so they cannot be heated to within 25° F. of their decomposition temperature or to 125° F., whichever is lower and in accordance with the manufacturer’s recommendations.
Outdoor storage and use areas for hazardous materials shall comply with the following:
- Outdoor storage and use areas shall be kept free of weeds, debris, and common combustible materials not necessary to the storage or use of hazardous materials.
- The area surrounding an outdoor storage and use area shall be kept clear of weeds, debris, and common combustible materials not necessary to the storage or use of hazardous materials for a minimum distance of 15 ft.
- Outdoor storage and use areas for hazardous materials shall be located not closer than 20 ft. from a property line that can be built upon, a street, an alley, or a public way, except that a 2-hour fire barrier wall, without openings and extending not less than 30 in. above and to the sides of the storage area, shall be permitted in lieu of such distance.
The following shall apply where oxidizers are in segregated storage with flammable and combustible liquids:
- The oxidizer containers and flammable and combustible liquid containers shall be separated by at least 25 ft.
- The separation shall be maintained by dikes, drains, or floor slopes to prevent flammable liquid leakage from encroaching on the separation.
Storage Quantities and Allowable Distances in a Non-sprinklered or Detached Building
Building Limit (lbs.) | Pile Limit (tons) | Storage Height (ft.) | Pile Width (ft.) | Max Distance from a container to an aisle (ft.) | Distance to wall (ft.) | Distance to incompatible Materials and Combustible Commodities | |
Class 3 | 40,000 | 5 | 6 | 12 | 8 | 4 | NP |
Class 2 | 100,000 | 10 | 8 | 16 | 8 | 4 | NP |
Class 1 | NL | 20 | 8 | 16 | 8 | 4 | NP |
NP = Not Permitted NL = No Limit NA = Not Applicable
Storage Quantities and Allowable Distances in a Sprinklered Detached Building
Building Limit | Pile Limit (tons) | Storage Height (ft.) | Pile Width (ft.) | Max Distance from a container to an aisle (ft.) | Distance to wall (ft.) | Distance to incompatible Materials and Combustible Commodities | |
Class 4* | NL | 8 | 4 | 8 | ** 75 ft. Ð 400 ft. | ||
Class 3 | NL | 100 | 20 | 20 | 10 | 2 | NP |
Class 2 | NL | 200 | 25 | 25 | 12 | 2 | NP |
Class 1 | NL | 200 | 20 | 24 | 12 | 2 | 8 ft. |
NP = Not Permitted NL = No Limit NA = Not Applicable
*In drums, containers and cases. Need Deluge System 0.35 gpm/ft2 over the entire storage area
**Separation of Buildings from Tanks per NFPA 400 Table 15.3.2.5.4.4
FM Global has adopted NFPA 400 (2013 edition) in their standard FM Global Property Loss Prevention Data Sheet 7-82N, Storage of Liquid and Solid Oxidizing Materials. An updated 2016 edition of NFPA 400 is available.
If you would like a review of storage practices for Oxidizers conducted at your facility please contact Risk Logic. We will work with you to determine acceptable options/alternatives.