# Cold boxes.

**Citation:** 49 CFR 193.2421  
**Type / status:** regulation / historical  
**Agency:** Pipeline and Hazardous Materials Safety Administration  
**Effective:** 1999-10-01  
**Published:** Not stated

(a) Each cold box in a liquefaction system must be equipped with a means of monitoring or detecting, as appropriate, the concentration of natural gas in the insulation space.

(b) If the insulation space in a cold box is designed to operate with a gas rich atmosphere, additional natural gas must be 

## Document text

(a) Each cold box in a liquefaction system must be equipped with a means of monitoring or detecting, as appropriate, the concentration of natural gas in the insulation space.

(b) If the insulation space in a cold box is designed to operate with a gas rich atmosphere, additional natural gas must be introduced when the concentration of gas falls to 30 percent.

(c) If the insulation space of a cold box is designed to operate with a gas free atmosphere, additional air or inert gas, as appropriate, must be introduced when the concentration of gas is 25 percent of the lower flammable limit.

## Provenance

- Official: Yes
- Source: <https://www.govinfo.gov/app/details/CFR-1999-title49-vol3/CFR-1999-title49-vol3-sec193-2421>
- Source ID: `govinfo-cfr`
- SHA-256: `0792d3a0e1f58bd9ece0eaff50d67c254436b7f7e028f2c6de7db3054d42d397`
- Retrieved: 2026-08-12T01:41:23.231Z
- Exported: 2026-08-24T05:45:53.922Z
- Document slug: `49-cfr-193-2421`

### Source metadata

```json
{
  "part": "193",
  "section": "193.2421",
  "subpart": "Subpart E—Equipment",
  "annualEdition": 1999,
  "revisedAsOf": "1999-10-01",
  "govInfoPackage": "CFR-1999-title49-vol3",
  "legalStatus": "official-annual-cfr-edition",
  "effectiveDateNote": null,
  "historicalAnchor": true,
  "historicalAnchorNote": "The section appears in an official annual CFR edition but is absent from the connected current eCFR corpus.",
  "jurisdiction": "US"
}
```