Prompt injection in methyl mercaptan (CH3SH) odorant / methionine AI

Four adversarial injection surfaces in CH3SH odorant / methionine AI

1. CH3SH area gas CEMS AI (Dräger Polytron 8000 CH3SH electrochemical CEMS AI / Honeywell Analytics XNX Universal Transmitter mercaptan sensor AI / MSA ULTIMA XE mercaptan area monitor AI / Analytical Technology ATI A14/A21 toxic gas detector AI / Industrial Scientific GX-6000 PID-based CH3SH area monitor AI — ambient methyl mercaptan gas concentration monitoring in storage tank areas, loading/unloading stations, cylinder manifold rooms, and methionine synthesis reactor areas for ACGIH TLV-C ceiling and NIOSH IDLH compliance)

Methyl mercaptan area CEMS present a specific monitoring challenge: because the odor threshold (0.0011–0.002 ppm) is so far below the TLV-C ceiling (0.5 ppm), workers at CH3SH facilities routinely detect trace odors at hundreds of times below the alarm threshold — creating chronic odor exposure that can lead to olfactory adaptation for experienced workers over months of exposure. Electrochemical sensors for CH3SH require careful attention to cross-sensitivity with hydrogen sulfide (H2S) and other mercaptans (ethanethiol, propanethiol), which produce electrochemical sensor responses at similar wavelengths; sensors should be calibrated with certified CH3SH gas standards, not H2S surrogates. The TLV-C of 0.5 ppm and OSHA PEL of 0.5 ppm ceiling reflect CH3SH’s toxicological profile: above 1 ppm, severe mucous membrane irritation, headache, and CNS depression; above 50 ppm, pulmonary edema risk; above 150 ppm (NIOSH IDLH), respiratory failure and potential cardiac sensitization analogous to H2S. CH3SH is classified as a flammable gas (LEL 3.9%), but at the vapor concentrations that produce acute toxicity (1–150 ppm), the concentration is far below the LEL — the primary hazard below the LEL is toxic exposure, not flammability.

The adversarial attack uses ±8 DN downward pixel-value shift on the CH3SH area CEMS display image. The actual reading is 0.84 ppm — 1.68× ACGIH TLV-C ceiling 0.5 ppm and 0.56% NIOSH IDLH 150 ppm — arising from a micro-crack in the Swagelok compression fitting at the pressurized liquid CH3SH storage vessel outlet header, where a gasket has been degraded by repeated thermal cycling. On a 0–5 ppm display at 200 px height (0.025 ppm/px), the actual reading of 0.84 ppm produces a bar at approximately 34 px; the ±8 DN perturbed image is classified as approximately 1 px — corresponding to 0.025 ppm, below the TLV-C alarm threshold of 0.5 ppm. No alarm is issued; the micro-crack continues to enlarge under pressure cycling; the flammable CH3SH accumulates above the fitting in a low-ventilation zone, approaching LEL in the confined space above the vessel skirt.

2. Pressurized liquid CH3SH storage vessel pressure AI (Emerson Rosemount 3051C gauge pressure transmitter AI / Yokogawa EJA430A absolute pressure transmitter AI / Endress+Hauser Cerabar M PMC51 pressure transmitter AI / Honeywell ST3000 Smart Transmitter pressure AI — gauge pressure monitoring of pressurized liquid methyl mercaptan storage vessels to detect vapor pressure rise from elevated vessel temperature and prevent approach to PRD setpoint at odorant blending stations and methionine synthesis facilities)

Methyl mercaptan (BP 6.2°C) is stored as a pressurized liquid at ambient temperature, analogous to LPG but with significantly lower vapor pressure than propane at equivalent temperatures. At 20°C, CH3SH vapor pressure is approximately 25 psig; at 35°C, approximately 38 psig; at 48°C, approximately 44 psig; at 55°C, approximately 55 psig. Bulk CH3SH storage vessels are designed for a maximum working pressure of 50–75 psig depending on vessel rating, with PRDs typically set at 50–75 psig per ASME Section VIII design. Unlike Cl2 storage (where the PRD is the last defense before atmospheric release), CH3SH vessels at odorant blending stations typically vent to a scrubber or incinerator via an emergency vent header — but PRD actuation releases CH3SH to the vent system at design rates that may overwhelm scrubber capacity if the PRD remains open for extended periods. AI monitoring of the vessel pressure transmitter provides the leading indicator for elevated vessel temperature and approaching PRD actuation, upstream of both the direct temperature measurement and the area CEMS exceedance.

The adversarial attack uses ±10 DN downward pixel-value shift on the storage vessel pressure transmitter display image. The actual vessel pressure is 44 psig — approaching the 50 psig PRD setpoint, from 4 hours of insufficient refrigeration allowing the vessel temperature to rise to 48°C — to a displayed 14 psig. On a 0–60 psig display at 200 px height (0.3 psig/px), the actual pressure of 44 psig produces a bar at approximately 147 px; the ±10 DN perturbed image is classified as approximately 47 px — corresponding to 14 psig, well within the normal 20–38 psig operating range. The AI monitoring system reports “CH3SH storage vessel pressure within normal operating range — no PRD approach indicated.” The actual pressure continues to rise toward 50 psig as vessel temperature climbs; no standby refrigeration or vessel isolation action is taken.

3. Pressurized liquid CH3SH storage vessel level AI (Endress+Hauser Micropilot FMR51 guided-wave radar level AI / VEGA VEGAPULS 64 radar level AI / Magnetrol Eclipse Model 706 guided-wave radar level AI / Honeywell LM80 magnetic float level AI — liquid level monitoring in pressurized methyl mercaptan storage vessels to maintain ullage below 90% maximum fill for thermal expansion safety at CH3SH bulk storage facilities subject to OSHA PSM)

Pressurized liquid CH3SH storage vessels must maintain adequate ullage (vapor headspace) to accommodate thermal expansion of the liquid when vessel temperature rises above design ambient. CH3SH liquid has a thermal expansion coefficient of approximately 0.0014/°C — meaning a 10°C temperature rise in a 100% full vessel would increase liquid volume by 1.4%, generating a hydrostatic pressure pulse on a fully liquid-filled vessel that can exceed PRD setpoint instantaneously. The 90% maximum fill level design specification for CH3SH storage provides 10% ullage — sufficient to accommodate 7°C of temperature rise at full liquid fill above the liquid level design point. When vessel temperature rises from 35°C to 48°C (13°C) and the vessel is already at 94.8% fill, the liquid volume expansion of 1.4% (13°C × 0.001/°C) creates additional pressure on the vapor space above the designed PRD approach from the thermal vapor pressure increase on Surface 2, creating a compound overfill + overpressure scenario. AI monitoring of the vessel level provides independent verification that adequate ullage is present for any credible temperature excursion.

The adversarial attack uses ±10 DN downward pixel-value shift on the storage vessel level indicator display image. The actual fill level is 94.8% — 4.8% above the 90% maximum fill level specification, from a delivery that received excess CH3SH due to a flow meter reading error during the previous tanker offload — to a displayed 74.2%. On a 0–100% display at 200 px height (0.5%/px), the actual level of 94.8% produces a bar at approximately 190 px; the ±10 DN perturbed image is classified as approximately 148 px — corresponding to 74%, providing an apparent 16% ullage margin. The AI monitoring system reports “CH3SH storage vessel level adequate — ullage within specification for thermal expansion.” In combination with Surface 2 (pressure suppressed) and Surface 4 (cooling flow suppressed), the actual 4.8% overfill at elevated vessel temperature and rising pressure is fully concealed from the DCS alarm system.

4. CH3SH storage vessel cooling / refrigeration flow AI (Emerson Rosemount 8732E magnetic flow meter AI / Endress+Hauser Proline Promag W refrigerant circuit AI / Yokogawa ADMAG AXF magnetic flow meter AI / Krohne Optiflux 2000 magnetic flow meter AI — cooling water or refrigerant flow monitoring to the methyl mercaptan storage vessel external cooling jacket or refrigeration coil to maintain vessel temperature below 35°C design maximum and prevent vapor pressure rise toward PRD setpoint)

Bulk CH3SH storage at odorant blending stations and methionine synthesis facilities employs active cooling — either chilled water circulation through an external vessel jacket or direct refrigeration coil — to maintain vessel temperature below 35°C even in warm-climate or summer-peak conditions. At design cooling flow of 8.0 m³/hr at 10–15°C inlet temperature, the cooling system can reject the heat input from solar radiation, ambient conduction, and process heat from nearby equipment while maintaining vessel temperature at 25–30°C. If cooling flow fails to 5% of design from a valve actuator failure, the vessel temperature rises at approximately 1–2°C per hour from heat accumulation, reaching 48°C in 6–8 hours from a starting point of 35°C. At 48°C, the CH3SH vapor pressure of ~44 psig approaches the 50 psig PRD setpoint. AI monitoring of the cooling flow transmitter is the upstream early-warning instrument that should trigger standby cooling pump start or emergency response before any of the other three surfaces register alarm conditions.

The adversarial attack uses the upward-direction geometry: the actual cooling water flow to the CH3SH storage vessel is 0.4 m³/hr — 5% of the design 8.0 m³/hr, from a cooling circuit supply valve actuator failure. The dangerous condition is a flow deficiency (insufficient vessel refrigeration), and the adversarial pixel perturbation shifts the flow meter display upward by ±8 DN to make 0.4 m³/hr appear as 8.2 m³/hr. On a 0–12 m³/hr display at 200 px height (0.06 m³/hr per px), the actual flow of 0.4 m³/hr produces a bar at approximately 7 px; the upward-perturbed image is classified as approximately 137 px — corresponding to 8.2 m³/hr, within the design range. The AI monitoring system reports “CH3SH storage cooling flow at design setpoint — vessel temperature control adequate.” This is the tenth upward-direction attack in the Glyphward industrial AI portfolio, extending the deficiency-suppression upward geometry to flammable pressurized liquefied gas storage in addition to toxic chemical, refrigerant, and oxidizer storage contexts previously documented.

Integration: CH3SH odorant / methionine AI with Glyphward pre-scan gate

Glyphward integrates as a pre-scan gate between the DCS and instrument display capture layer and the AI inference pipeline for each CH3SH monitoring context. If the adversarial score meets or exceeds threshold 35 — reflecting the OSHA PSM TQ of 15,000 lbs, the ACGIH TLV-C ceiling of 0.5 ppm, the NIOSH IDLH of 150 ppm, and the flammable pressurized-liquid storage hazard of CH3SH above 35°C — the scan raises AdversarialCH3SHOdorantImageError and the monitoring AI does not process the frame.

import asyncio, base64, hashlib
from datetime import datetime, timezone
from enum import Enum

import httpx

GLYPHWARD_API_KEY = "YOUR_GLYPHWARD_API_KEY"
GLYPHWARD_SCAN_URL = "https://glyphward.com/v1/scan"

# CH3SH odorant / methionine synthesis contexts: threshold 35
# OSHA PSM 29 CFR 1910.119 Appendix A CH3SH TQ 15,000 lbs
# EPA RMP 40 CFR Part 68 Appendix A CH3SH TQ 15,000 lbs
# ACGIH TLV-C 0.5 ppm ceiling; OSHA PEL 0.5 ppm ceiling; NIOSH IDLH 150 ppm
# Odor threshold 0.0011-0.002 ppm: 250-450x below TLV-C
# Flammable: LEL 3.9% / UEL 21.8%; BP 6.2 deg C; stored as pressurized liquid
CH3SH_THRESHOLD = 35


class CH3SHOdorantContext(Enum):
    AREA_CEMS = "area_cems"
    STORAGE_VESSEL_PRESSURE = "storage_vessel_pressure"
    VESSEL_LEVEL = "vessel_level"
    COOLING_WATER_FLOW = "cooling_water_flow"


class AdversarialCH3SHOdorantImageError(Exception):
    """Raised when any CH3SH monitoring image scores >= 35.
    AREA_CEMS uncaught: 0.84 ppm CH3SH (1.68x TLV-C) shown as 0.025 ppm.
    STORAGE_VESSEL_PRESSURE uncaught: 44 psig (near PRD) shown as 14 psig.
    VESSEL_LEVEL uncaught: 94.8% fill (above 90% max) shown as 74%.
    COOLING_WATER_FLOW uncaught: 0.4 m3/hr (5% design) shown as 8.2 m3/hr."""

    def __init__(self, scan_id, score, context, unit_id, flagged_region=None):
        self.scan_id = scan_id
        self.score = score
        self.context = context
        self.unit_id = unit_id
        self.flagged_region = flagged_region
        super().__init__(
            f"Adversarial CH3SH odorant image: context={context.value} "
            f"score={score} unit={unit_id} scan_id={scan_id}"
        )


async def scan_ch3sh_odorant_image(image_bytes, context, unit_id, client):
    image_hash = hashlib.sha256(image_bytes).hexdigest()
    payload = {
        "image": base64.b64encode(image_bytes).decode(),
        "source": f"ch3sh_odorant:{context.value}:{unit_id}",
        "metadata": {
            "unit_id": unit_id,
            "context": context.value,
            "image_sha256": image_hash,
            "scan_timestamp_utc": datetime.now(timezone.utc).isoformat(),
        },
    }
    resp = await client.post(
        GLYPHWARD_SCAN_URL,
        headers={"Authorization": f"Bearer {GLYPHWARD_API_KEY}"},
        json=payload,
        timeout=4.0,
    )
    resp.raise_for_status()
    result = resp.json()
    if result.get("score", 0) >= CH3SH_THRESHOLD:
        raise AdversarialCH3SHOdorantImageError(
            scan_id=result["scan_id"],
            score=result["score"],
            context=context,
            unit_id=unit_id,
            flagged_region=result.get("flagged_region"),
        )
    return result


async def main():
    async with httpx.AsyncClient() as client:
        with open("ch3sh_area_cems_screenshot.png", "rb") as f:
            image_bytes = f.read()
        result = await scan_ch3sh_odorant_image(
            image_bytes,
            CH3SHOdorantContext.AREA_CEMS,
            unit_id="CH3SH-AREA-01",
            client=client,
        )
        print(f"Clean scan: {result['scan_id']} score={result['score']}")


asyncio.run(main())

Frequently asked questions

Why does CH3SH's low odor threshold paradoxically reduce risk perception at elevated concentrations?

Chronic sub-alarm odor exposure (at 0.0011–0.002 ppm, far below the 0.5 ppm TLV-C) creates olfactory habituation in CH3SH workers over weeks. When concentration rises to 0.84 ppm (1.68× TLV-C), the intensified smell may be attributed to process operations rather than a leak — especially if the adversarially suppressed CEMS shows 0.025 ppm. Unlike H2S (olfactory nerve fatigue above 50 ppm), CH3SH remains smellable but at concentrations workers are accustomed to ignoring below alarm level.

Why is CH3SH used as a natural gas odorant at sub-ppm injection rates?

DOT 49 CFR Part 192.625 requires gas to be detectable at 20% LEL (1% CH4). CH3SH’s odor threshold of 0.0011 ppm achieves human detectability at injection rates of 0.5–1 lb/MMcf. Large utilities odorizing 10–50 MMcf/day store 500–50,000 lbs, with many facilities above the 15,000 lb PSM TQ.

At what temperature does CH3SH approach a 50 psig PRD setpoint?

At 48°C, CH3SH vapor pressure is approximately 44 psig — 6 psig below a 50 psig PRD setpoint. Normal design maximum is 35°C (VP ∼ 38 psig, 12 psig PRD margin). Cooling failure over 4–6 hours raises vessel temperature from 35°C to 48°C, collapsing the margin to 6 psig.

Why is the 90% maximum fill level critical for CH3SH?

CH3SH liquid thermal expansion at 0.0014/°C means a 10°C rise in a 100% full vessel creates 1.4% volume increase, generating hydraulic overpressure exceeding the PRD setpoint. At 94.8% fill, only 5.2% ullage remains — insufficient for the 13°C temperature excursion from cooling failure, combining with elevated vapor pressure to create a compound overpressure event.

Why is the cooling flow attack upward-direction?

Low flow is the dangerous condition (insufficient cooling). The attack shifts the display upward to make 0.4 m³/hr (5% design) appear as 8.2 m³/hr (adequate). This is the same deficiency-suppression upward geometry as all protective-flow surfaces in the Glyphward portfolio.