5.1 Most heated apparatus in industrial, commercial, and residential service are insulated, unless thermal insulation would interfere with their function; for example, it is inappropriate to insulate the bottom surface of a flatiron. However, surface temperatures of insulated equipment and appliances may still be high enough to cause burns from contact exposure under certain conditions.

5.2 This guide has been developed to standardize the determination of acceptable surface operating conditions for heated systems. Current practice for this determination is widely varied. The intent of this guide is to tie together the existing practices into a consensus standard based upon scientific understanding of the thermal physics involved. Flexibility is retained within this guide for the designer, regulator, or consumer to establish specific burn hazard criteria. Most generally, the regulated criterion will be the length of time of contact exposure.

5.3 It is beyond the scope of this guide to establish appropriate contact times and acceptable levels of injury for particular situations, or determine what surface temperature is “safe.” Clearly, quite different criteria may be justified for cases as diverse as those involving infants and domestic appliances, and experienced adults and industrial equipment. In the first case, no more than first degree burns in 60 s might be desirable. In the second case, second degree burns in 5 s might be acceptable.

5.4 This guide is meant to serve only as an estimation of the exposure to which an average individual might be subjected. Unusual conditions of exposure, physical health variations, or nonstandard ambients all serve to modify the results.

5.5 This guide is limited to contact exposure to heated surfaces only. It should be noted that conditions of personal exposure to periods of high ambient temperature or high radiant fluxes may cause human injury with no direct contact.

5.6 This guide is not intended to cover hazards for cold temperature exposure, that is, refrigeration or cryogenic applications.

5.7 The procedure found in this guide has been described in the literature as applicable to all heated surfaces. For extremely high-temperature metallic surfaces (>70°C), damage occurs almost instantaneously upon contact.

1.1 This guide covers a process for the determination of acceptable surface operating conditions for heated systems. The human burn hazard is defined, and methods are presented for use in the design or evaluation of heated systems to prevent serious injury from contact with the exposed surfaces.

1.2 The maximum acceptable temperature for a particular surface is derived from an estimate of the possible or probable contact time, the surface system configuration, and the level of injury deemed acceptable for a particular situation.

1.3 For design purposes, the probable contact time for industrial situations has been established at 5 s. For consumer products, a longer (60-s) contact time has been proposed by Wu (1)² and others to reflect the slower reaction times for children, the elderly, or the infirm.

1.4 The maximum level of injury recommended here is that causing first degree burns on the average subject. This type of injury is reversible and causes no permanent tissue damage. For cases where more severe conditions are mandated (by space, economic, exposure probability, or other outside considerations), this guide may be used to establish a second, less desirable injury level (second degree burns), where some permanent tissue damage can be permitted. At no time, however, are conditions that produce third degree burns recommended.

1.5 This guide addresses the skin contact temperature determination for passive heated surfaces only. The guidelines contained herein are not applicable to chemical, electrical, or other similar hazards that provide a heat generation source at the location of contact.

1.6 A bibliography of human burn evaluation studies and surface hazard measurement is provided in the list of references at the end of this guide (1-16).

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all 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 its use.