Any chamber application is considered hazardous where the workload being heated can combine with the atmosphere around it to produce an explosive mixture such as when working with paints, lacquers, solvents and similar materials.

Blue M offers three lines of safety chambers for hazardous applications:

• Friction-aire
• Class A Batch Ovens
• CSP Safety Ovens

There are two basic classifications of hazardous atmospheres that affect chamber selection.

• Class I involves atmospheres containing flammable gases or vapors.
• Class II pertains to atmospheres containing combustible dust.

Atmospheres containing solvents normally used in finishing are classified specifically as Class I, Group D.

This classification means that an area has enough flammable Group D solvent vapors present to produce an ignitable mixture in the atmosphere.

Any electrical device or wiring in such an area must be totally enclosed in a suitable enclosure. It must be strong enough to withstand an explosion ignited internally by an electrical spark and can not disintegrate or allow a flame to reach the external atmosphere. In addition, no exposed surface of the enclosure can exceed +215° C, the auto-ignition temperature of the lowest of Group D solvents.

The current standard covering chamber safety features is found in the National Fire Codes prepared by the National Fire Protection Association (NFPA). This includes:

Bulletin 70, National Electrical Code
Bulletin 86, Class A Ovens and Furnaces

NFPA fire codes

These are advisory documents that have been adopted in whole or in part by various city and state governmental codes, insurance agencies (such as F.I.A. -- Factory Insurance Association and F.M. -- Factory Mutual), and by OSHA. But, there is no formally OSHA-approved or F.I.A.approved oven on the market.

Compliance procedure

An oven buyer must define the hazardous material to be processed and determine the volatile load that must be processed.

The chamber manufacturer must define the specific unit offered for the application and its safety features, wiring diagram and exhaust rates.