What is Texas RRC Rule 36?

Texas Railroad Commission Statewide Rule 36 (16 TAC §3.36) governs oil and gas operations involving hydrogen sulfide in Texas. It requires operators to calculate the Radius of Exposure for wells and facilities handling gas with H2S, submit contingency plans when the ROE reaches populated areas, and maintain specific safety equipment and training standards. It is the primary H2S regulation for Texas operations, including the Permian Basin Texas side.

What is the Rule 36 formula for 100 ppm ROE?

The 100 ppm ROE formula under 16 TAC §3.36 is: x = [(1.589)(mole fraction H2S)(Q)]^0.6258, where x is the radius in feet, mole fraction H2S is the decimal H2S concentration in the escaping gas, and Q is the maximum volume of gas available for escape in cubic feet per day at standard conditions. The 500 ppm ROE uses a coefficient of 0.4546 instead of 1.589, with the same exponent.

When is a contingency plan required under Rule 36?

Rule 36 requires a contingency plan when the 100 ppm radius of exposure reaches a public area — including dwellings, roads, churches, schools, parks, or other places of assembly. The specific triggers depend on the proximity to populated areas and the magnitude of the ROE. Operators must file the contingency plan with the RRC and coordinate with local emergency responders.

What counts as Q — the escape volume?

Q is the maximum volume of gas that could be available for escape at standard conditions (cubic feet per day). For gas wells, this is typically the 24-hour absolute open flow (AOF) rate. For producing wells and facilities, it's the daily production rate. For pipelines, it's the maximum throughput. The appropriate Q value depends on the equipment and operation being evaluated — consult a qualified engineer for site-specific determination.

Does the ROE calculation account for wind and topography?

No. The Rule 36 formula gives one radius in every direction and does not use wind speed, wind direction, or terrain. That is why this tool adds a wind plume snapshot: enter the wind from your weather app and it estimates which way the gas goes and how far the 500, 100 and 10 ppm levels reach. It still does not model terrain. For detailed emergency planning, operators use dispersion models such as ALOHA.

How does the wind plume snapshot work?

It uses a Gaussian plume model for a continuous ground-level release, with Briggs rural dispersion coefficients and Pasquill stability classes picked from the wind speed, time of day and sky cover. ALOHA, the free EPA and NOAA tool, uses the same approach for gases that are not heavier than air. The faint wedge around the plume covers a wind swing of one compass point either side, and nearby roads and homes are checked against the worst direction in that range. It assumes flat open ground and a steady wind, so treat it as a screening estimate and confirm with gas monitors.

Does a stronger wind push H2S farther?

Not at the same concentration. A stronger wind carries gas in one direction faster, but it also dilutes it faster, so the 100 ppm zone usually gets shorter. The longest reach is usually a light wind on a clear night, when the air is stable and gas stays near the ground. A stronger wind does get gas to a road or home sooner, which is why the tool shows arrival time.

What unit should I use for escape volume?

Use whatever your production data uses. The calculator defaults to Mcf/d (thousand cubic feet per day) and also accepts MMcf/d and cubic feet per day. The Rule 36 formula itself uses cubic feet per day, so 1,000 Mcf/d is entered into the formula as 1,000,000.

What are the OSHA exposure limits for H2S?

OSHA's permissible exposure limits for hydrogen sulfide are: acceptable ceiling concentration of 20 ppm, acceptable maximum peak of 50 ppm for up to 10 minutes per 8-hour shift, with no other measurable exposure at the peak concentration. The ACGIH TLV-TWA is 1 ppm and the STEL is 5 ppm. NIOSH lists 100 ppm as the IDLH (Immediately Dangerous to Life or Health) concentration.

Does New Mexico have a similar H2S rule?

Yes. The New Mexico Oil Conservation Division (OCD) has its own H2S rules (19.15.11 NMAC) that are similar in principle to Texas Rule 36 but with some differences in formulas, triggers, and contingency plan requirements. Operators in the New Mexico side of the Permian Basin should reference the OCD rules directly. This calculator uses the Texas RRC formula, which is commonly adapted for planning in both jurisdictions but is not a substitute for actual NM OCD compliance.

What safety equipment is required for sour operations?

At a minimum: personal H2S monitors for all workers, fixed H2S detection at key equipment, SCBA (self-contained breathing apparatus) or supplied-air respirators staged at the worksite, wind direction indicators, evacuation alarms, and a documented muster point upwind of the potential release. All personnel entering the area require current H2S training per ANSI Z390.1. A written H2S safety program is required under OSHA's General Duty Clause 5(a)(1) and under Rule 36 for covered operations.

Can I rely on this calculator for actual compliance?

No. This calculator is a planning estimate only. Actual compliance with RRC Rule 36, OSHA H2S requirements, and NM OCD rules requires a qualified engineer or safety professional to perform site-specific assessment, verify inputs against authoritative gas analysis data, and sign off on contingency plans. Use this tool for initial planning, to understand what the formula produces for typical scenarios, and as a starting point for engineering consultation.

H2S Radius of Exposure Calculator

Calculate the 100 ppm and 500 ppm hydrogen sulfide radius of exposure with the Texas Railroad Commission Rule 36 formula (16 TAC §3.36), then enter the current wind to see which way the gas goes, how far each concentration reaches, and which roads and homes are in the way. Built for the field and for first responders. Screening estimates only, not a substitute for a qualified engineer's contingency plan or gas monitoring.

100 ppm ROE vs public areas

500 ppm ROE vs public roads

Wind plume snapshot

H2S Radius of Exposure and Wind Plume

Step 1: the Texas RRC Rule 36 radius of exposure (16 TAC §3.36). Step 2: where the gas goes with today's wind. Step 3: which roads and buildings are in the way. Planning and screening estimates only.

Screening estimate only. Contingency planning for sour operations needs a qualified engineer with site-specific data. During a release, gas monitors and your emergency response plan come first. This is not legal or engineering advice.

H2S in gas stream

From your gas analysis

Escape volume

Most gas available to escape: AOF for gas wells, production rate for producing wells.

Wind plume snapshot

The Rule 36 radius assumes the gas could go any direction. Enter the wind from your weather app to see which way it goes and how far each concentration reaches. Update the wind and it redraws.

Wind speed (mph)

Wind from

Time of day

Sky

Release source and advanced settings

What is releasing

Atmospheric stability

Enter the H2S concentration and escape volume in step 1 to draw the plume.

Roads, homes and access routes

Add what is around the release point by direction and distance. Each one is checked against the Rule 36 radius and the wind plume, including arrival time.

Name

Type

Direction

Distance (ft)

Download H2S Program Template H2S Drill Builder

ROE formula (Texas RRC Rule 36, 16 TAC §3.36): ROE = [coefficient × mole_fraction_H2S × Q]^0.6258, coefficient 1.589 for 100 ppm and 0.4546 for 500 ppm, Q in cubic feet per day. Wind plume: Gaussian plume for a continuous ground-level release with Briggs rural dispersion coefficients and Pasquill stability classes, the same approach ALOHA uses for gases that are not heavier than air. It assumes flat open ground and a steady wind, and does not model terrain, buildings, dense gas, or jet releases.

Rule 36 Formula Explained

100 ppm ROE = [1.589 × mole fraction H2S × Q]^0.6258

500 ppm ROE = [0.4546 × mole fraction H2S × Q]^0.6258

Mole Fraction H2S

Decimal fraction of H2S in escaping gas (e.g., 5% = 0.05). From your gas analysis.

Q (Escape Volume)

Cubic feet per day at standard conditions. Typically AOF rate for gas wells or daily production rate.

Example: A gas well with 5% H2S and 5,000,000 cubic feet/day escape volume produces a 100 ppm ROE of approximately 3,191 feet (0.60 miles). That is over 3,000 feet, so Rule 36 requires a contingency plan regardless of what lies inside the radius. The 500 ppm ROE is approximately 1,458 feet.

When You Need to Calculate ROE

Before Drilling Sour Wells

Required during well permitting for any location expected to encounter H2S. The ROE drives setback requirements and contingency plan scope.

Production Facility Planning

Tank batteries, separators, and flow lines handling sour gas require ROE assessment for each release scenario and each piece of equipment.

Rule 36 full text

The complete Texas Administrative Code 16 TAC §3.36 is available on the Texas RRC website. Always reference the current authoritative version for compliance decisions.

Don't Stop at the ROE — Document the Whole Program

The ROE is one piece of H2S compliance. OSHA and the RRC also require a written H2S safety program, SCBA-equipped personnel, monitoring, training records, and a contingency plan. BasinCheck gives you the written program template and the documentation system to prove it's in place.

Written Program

Free H2S safety program template aligned with ANSI Z390.1 and OSHA General Duty Clause 5(a)(1).

Training Records

Track H2S training, monitor certifications, SCBA fit-test dates, and refresher requirements.

Inspection Logs

Document atmospheric monitoring, equipment checks, drills, and corrective actions.

Free H2S Program Template H2S Drill Builder H2S Release for teams (beta)

H2S Radius of Exposure FAQ

Common questions about H2S ROE calculations and Texas RRC Rule 36

The Radius of Exposure is the horizontal distance from a potential H2S release point at which hydrogen sulfide concentrations in ambient air would equal a specified threshold, typically 100 ppm and 500 ppm. Under Texas Rule 36, a contingency plan is required when the 100 ppm ROE (at least 50 ft) includes any part of a public area, when the 500 ppm ROE (at least 50 ft) includes any part of a public road, or when the 100 ppm ROE is over 3,000 ft.

Sour Operations Need Sharp Documentation

BasinCheck gives you the written programs, training records, and inspection logs that operators, OSHA, and the RRC expect for H2S operations.

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