Status Report

NASA Lessons Learned: ISS Program/Hazardous Materials Containment/Payload Toxic Substance Sensing

By SpaceRef Editor

October 3, 2003

Filed under ISS, NASA Public Lessons Learned System (PLLS) Database, US

PLLS Database Entry: 1018

Lesson Info

* Lesson Number: 1018
* Lesson Date: 01-feb-1997
* Submitting Organization: HQ
* Submitted by: David M. Lengyel

Subject/Title/Topic(s):

International Space Station (ISS) Program/Hazardous Materials Containment/Payload Toxic Substance Sensing

Description of Driving Event:

Payload Requirements for Hazardous Materials Containment

Lesson(s) Learned:

The ISS has no requirement for sensing a toxic substance spill within a payload rack. The ISS does require that toxic substances in payload racks be multiply contained.

Recommendation(s):

The ISS should require payload providers to include, as part of their system design, detection and annunciation of any toxics they carry or could generate.

Evidence of Recurrence Control Effectiveness:

NASA concurs. The approach for payloads on the ISS is patterned after the Shuttle approach. The payload design requirements are defined in NSTS 1700.7B, “Safety Policy and Requirements for Payloads Using the Space Transportation System,” and the ISS Addendum, which to date make the possibility of having a toxic spill so remote as to be an acceptable risk. Requirements imposed on payloads include containment levels stipulated based on level of toxicity of the substance or use of an approved pressure vessel.

The payload provider is required to obtain approval by the Payload Safety Review Panel (PSRP) for the use of any toxic substance, as well as the containment method utilized. Through the safety process defined in NSTS 13830, “Implementation Procedure for STS Payloads System Safety Requirements,” all potentially toxic substances are labeled and documented in crew procedures, along with any cleanup instructions. This ensures that needed information on any potentially toxic substance is readily available to the crew. This concept for the handling of toxic substances is based on Shuttle and MIR program experience and has not been changed.

When payloads are reviewed by the PSRP, compliance with the above requirements must be demonstrated. Astronaut training and procedures are reviewed and approved to ensure that the crew is adequately educated to avoid inadvertently mixing toxic chemicals. In addition, the payload design must still be able to tolerate the appropriate number of operator errors.

These requirements do not impose design solutions on payloads; rather, they require the payload providers to proactively consider their own design solutions to avoid toxic mixing. Enforcing these requirements in the PSRP process by ensuring compliance with the requirements of NSTS 1700.7B will restrict the possibility for toxic mixing to an acceptable risk. Dependent on a case-by-case analysis, the PSRP or the payload provider may request detection and monitoring. The detection will then be provided by the payload provider organization with tie-in to the ISS core systems of C&W (annunciation) provided by core system interfaces at the rack level. This service will then be defined in the appropriate Interface Definition Document (IDD).

The crew will be used to enunciate any toxic spills throughout the ISS. This is considered essentially the equivalent of the panic alarm. The crew will also be used to detect any toxic spill. Studies have shown that intermodule ventilation will spread any toxic gases to all elements of the ISS within 20 minutes, which makes station-level detection not practical.

This further illustrates the importance of having adequate design requirements imposed on payloads to preclude toxic spills. Crew annunciation and detection have been considered acceptable because of the design requirements imposed on the payloads to maintain appropriate levels of containment. However, should a toxic spill occur, provisions are available to payloads for cleanup. These include a crew contamination protection kit (goggles, chemical resistant bags, chemical resistant gloves, emergency eyewash), a portable breathing apparatus, a combustion products analyzer, a volatile organics analyzer, multiple airborne trace contaminant control equipment, vacuum access, and module depressurization. The JSC Mission Operations Directorate is currently developing procedures to respond to a toxic spill. The procedures will be based on Shuttle experience. The response will depend on the hazard level of the substance, the state of the substance (liquid, gas, or solid), the location of the spill, and the size of the spill.

Applicable NASA Enterprise(s):