It is possible that the user of FR protective clothing will experience repeated exposures to hot air as part of the work environment. While these individual exposures are likely not to pose a catastrophic threat, the cumulative effect of these exposures are likely to reduce the level of retained sewn seam strength performance to a value that is measurably lower than the sewn seam strength performance requirement established for a new item.

The assembly of textile structures requires that the seam engineering used to manufacture the product anticipate how to retain the maximum sewn seam strength during the anticipated life cycle of the product.

Initial sewn seam strength performance requirements of FR textile products measures sewn seam strength of a new (never exposed to heat environment) product.

Retained sewn seam strength (RSS₅₀) can be used to measure seam failure of FR protective clothing after repeated short duration exposures to high heat. RSS₅₀ can also be used to measure seam failure of FR protective clothing when exposed to open flame after repeated short duration exposures to high heat.

These data about retained sewn seam strength are useful to establish criteria to determine when to repair, retire, or replace FR protective clothing.

1.1 This specification covers the retained sewn seam strength of flame resistant fabric subassemblies after repeated short duration exposures to hot air or repeated short-duration exposures to hot air and subsequent short-term exposures to open-flame impingement.

1.1.1 This specification is used to determine minimum retained sewn seam strength after these exposures.

1.2 This standard is not intended to serve as a detailed manufacturing or purchasing specification, but can be referenced in purchase contracts to ensure that minimum performance requirements are met.

1.3 Controlled laboratory tests used to determine compliance with the performance requirements of this standard shall not be deemed as establishing performance levels for all situations to which wearers of FR protective clothing are potentially exposed.

1.4 Mandatory requirements are indicated by use of shall; recommendations and advising information is indicated by should.

1.5 This standard is used to measure and describe the response of materials, products, or assemblies to heat and flame under controlled conditions, but does not by itself incorporate all factors required for fire hazard or fire risk assessment of the materials, products, or assemblies under actual fire conditions.

1.6 Fire testing is inherently hazardous. Adequate safeguards for personnel and property shall be employed in conducting these tests.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use.