External sparks

Nonconductive plastic pipe should not be used for transfer of ignitable powder or for any powder transfer through electrically classified areas. Hazards comprise brush discharges, PBDs and external sparks due to induction. Charge accumulation is discussed in 5-3.2.1. 

Iron Mass and Iron Sponge. Consist of a mixture of wood shavings with iron oxide and possibly lime or other material. If properly made and all the iron is properly oxidised, the material is free from the hazard of spontaneous heating or ignition. If there is an undue amount of metallic unoxidised iron, further oxidisation is liable to occur, producing sufficient heat in closely packed material to cause fire. This material may be ignited by external sparks. Iron mass is used for gas purification. lATA App. A... 

Ignition The intfoduction of some external spark, flame, or glowing object that initiates self-sustained combustion. 

Examples Diamond converts to graphite (infinitesimally slow rate). Iron rusts in air (very slow, but noticeable change). 2H2(g) + 02(g) -> 2H20(g) (very fast reaction or explosion with an external spark). 

This region is often referred to as the Townsend breakdown region, in which — with little or no further change in voltage — the current can rise by several orders of magnitude, e.g., from Kh to 10" A. There is usually a spark produced during the initiation of this process. The current flow is controlled by the size of the resistance in the external voltage circuit. 

The ignition temperature or autoignition temperature is the minimum temperature of a flammable mixture that is required to initiate or cause self-sustained combustion without ignition from an external source of energy such as a spark or flame (ASTM D2155). 

The dust-ignition-proof protection concept excludes dust from entering the device enclosure and will not permit arcs, sparks, or heat generated by the device to cause ignition of external suspensions or accumulations of the dust. Enclosure requirements can be found in ANSI/UL 1203-1994, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous Locations. ... 

The antoignition temperatnre of a gas or vapor is the minimnm temperatnre at which it will ignite in air withont any external sonrce of ignition (e.g., a flame, spark, hot snrface etc.). It is often also called the spontane-ons-ignition or self-ignition temperatnre. The measnrement of AIT depends on many factors, snch as molecnlar stmctnre of the gas/vapor. 

Deflagrations can be initiated by external stimuli such as shock, friction, or sparks. 

Explosives are generally detonated with the assistance of initiating devices (initiators) that are activated by external stimulation sources (friction, spark, or flame), and may include (1) primers, (2) detonators, (3) electric detonators, (4) safety fuses, and (5) detonating cord. 

Normally the heat to start a fire is supplied by an external source (ignition source). Once started, the heat from the fire reaction provides enough of its own heat to make the fire self-sustaining. A gas or vapor may be ignited by a small spark, while a solid may require a more intense source. 

---