1910.253(e)(3)(ii): Backflow, Flashback and Back-Pressure Devices
Employers must install approved protective equipment in fuel-gas piping to prevent oxygen backflow, flashback and excessive oxygen back pressure into the fuel-gas supply. Devices go in the main supply line, at each branch line head or at each withdrawal point. The pressure-relief device must be set no higher than the lower rating of the backflow or flashback device, sit downstream of them, and vent safely without moisture-collecting low points.
Key takeaways
- 1910.253(e)(3)(ii) is part of OSHA's general industry standards (29 CFR Part 1910, Subpart Q).
- OSHA cited it 25 times in the last 3 years, in 25 inspections, with $131,755 in current penalties.
- 1 death is linked to inspections that cited this rule.
- Most citations: NJ (20), IL (2), AL (1).
- Related part: 1910.253(e) Protective equipment, hose, and regulators (54 citations).
- Free 5-minute toolbox talk for your crew below.
In this article
What this rule covers
29 CFR 1910.253(e)(3)(ii) is one requirement inside 1910.253 Oxygen-fuel gas welding and cutting, an OSHA general industry standard (Part 1910, Subpart Q). It includes 3 sub-paragraphs. The official text below is copied word for word from the Electronic Code of Federal Regulations (eCFR). The numbers, injury cases and training on this page show how OSHA enforces it on real job sites.
Official text
(ii) Approved protective equipment (designated PF in Figures Q-1, Q-2, and Q-3) shall be installed in fuel-gas piping to prevent: 25 citations
(A) Backflow of oxygen into the fuel-gas supply system;
(B) Passage of a flash back into the fuel-gas supply system; and
(C) Excessive back pressure of oxygen in the fuel-gas supply system. The three functions of the protective equipment may be combined in one device or may be provided by separate devices. Open (e)(3)(ii)(c) 24 citations
(1) The protective equipment shall be located in the main supply line, as in Figure Q-1 or at the head of each branch line, as in Figure Q-2 or at each location where fuel-gas is withdrawn, as in Figure Q-3. Where branch lines are of 2-inch pipe size or larger or of substantial length, protective equipment (designated as PF) shall be located as shown in either Q-2 and Q-3.
(2) Backflow protection shall be provided by an approved device that will prevent oxygen from flowing into the fuel-gas system or fuel from flowing into the oxygen system (see SF, Figures Q-1 and Q-2).
(3) Flash-back protection shall be provided by an approved device that will prevent flame from passing into the fuel-gas system.
(4) Back-pressure protection shall be provided by an approved pressure-relief device set at a pressure not greater than the pressure rating of the backflow or the flashback protection device, whichever is lower. The pressure-relief device shall be located on the downstream side of the backflow and flashback protection devices. The vent from the pressure-relief device shall be at least as large as the relief device inlet and shall be installed without low points that may collect moisture. If low points are unavoidable, drip pots with drains closed with screw plugs or caps shall be installed at the low points. The vent terminus shall not endanger personnel or property through gas discharge; shall be located away from ignition sources; and shall terminate in a hood or bend.
Source: eCFR, text current as of 2026-10-15. Read all of 1910.253.
Injuries linked to this rule
1 death is linked to inspections where OSHA cited 1910.253(e)(3)(ii).
At 4:00 p.m. on October 22, 2024, an employee working as a machine maintenance technician was on an inclined conveyor preparing to maintain its gearbox. The employee was on top of the "naturals" conveyor (#C8) associated with the Colorbiotics mulch dye machine while a coworker…
Where and how often it was cited
| Year | Citations |
|---|---|
| 2023 | 1 |
| 2024 | 11 |
| 2025 | 5 |
| 2026 | 8 |
Top states: NJ (20), IL (2), AL (1), VT (1), OH (1)
Largest penalties
| Employer | Location | Penalty for this rule |
|---|---|---|
| RESOURCE RECYCLING, INC. | LIMA, OH | $11,585 |
| HACKETTSTOWN PUBLIC SCHOOLS | HACKETTSTOWN, NJ | $7,000 |
| NJ DEPARTMENT OF ENVIRONMENTAL PROTECTION | COLUMBIA, NJ | $7,000 |
| NEW JERSEY TURNPIKE AUTHORITY | MULLICA HILL, NJ | $7,000 |
| BOROUGH OF GLASSBORO PUBLIC SCHOOL DISTRICT | GLASSBORO, NJ | $7,000 |
Free toolbox talk
A 5-minute crew talk on 1910.253(e)(3)(ii), plus alerts when this rule changes. Free.
OSHA interpretation letters
None exist. OSHA has not published a letter of interpretation for 1910.253(e)(3)(ii).
Related parts of this rule
- 1910.253(e) Protective equipment, hose, and regulators 54 citations
- 1910.253(e)(3) Piping protective equipment 25 citations
- 1910.253(e)(3)(ii)(C) 24 citations
- 1910.253(e)(6) Pressure-reducing regulators 20 citations
- 1910.253(e)(6)(ii) 19 citations
Get your crew competent
Trainers on Black Belt Safety: Marc Harvey
Trainers and suppliers: feature your business on this rule for $25/month.
Frequently asked questions
Where can the protective equipment be located?
In the main supply line, at the head of each branch line, or at each location where fuel gas is withdrawn, per Figures Q-1, Q-2 and Q-3.
What about large branch lines?
Where branch lines are 2-inch pipe size or larger or of substantial length, the equipment must be located as in Figure Q-2 or Q-3.
What if the relief vent has low points?
If unavoidable, drip pots with drains closed by screw plugs or caps must be installed there.
About this page
Sources
- 29 CFR 1910.253 (eCFR), text current as of 2026-10-15
- U.S. Department of Labor enforcement data: OSHA inspections, citations and accident records, copied nightly; data as of 2026-10-25
3-year window. Federal OSHA only; state-plan rules are not counted. Plain-language text is a summary, not legal advice; the official text controls. Black Belt Safety is not part of OSHA or the Department of Labor.