Pixtral 12B — Construction Safety VQA

A fine-tuned Pixtral 12B for construction site hazard detection and classification. Distilled from Qwen3.5-27B teacher annotations using LoRA, this model outputs structured JSON with bounding boxes, severity levels, and bilingual (EN/JP) descriptions.

Built for Mistral EvoBoard — an AI Safety Committee that runs multi-agent debates on construction site images.

Key Results

Evaluated on 50 COCO-format hardhat detection test images. The model dramatically improves violation recall — the ability to detect missing PPE — which is the most safety-critical metric.

Usage

With vLLM (recommended)

vllm serve a1273352/pixtral-12b-construction-safety \
  --tensor-parallel-size 2 \
  --max-model-len 8192 \
  --port 8200

from openai import OpenAI

client = OpenAI(base_url="http://localhost:8200/v1", api_key="dummy")

response = client.chat.completions.create(
    model="a1273352/pixtral-12b-construction-safety",
    messages=[{
        "role": "user",
        "content": [
            {"type": "image_url", "image_url": {"url": "https://example.com/site.jpg"}},
            {"type": "text", "text": VISION_PROMPT},  # see below
        ],
    }],
    max_tokens=4096,
    temperature=0.1,
)

With Transformers

from transformers import AutoProcessor, LlavaForConditionalGeneration
from PIL import Image

model = LlavaForConditionalGeneration.from_pretrained(
    "a1273352/pixtral-12b-construction-safety",
    torch_dtype="bfloat16",
    device_map="auto",
)
processor = AutoProcessor.from_pretrained("a1273352/pixtral-12b-construction-safety")

image = Image.open("construction_site.jpg")
inputs = processor(text=VISION_PROMPT, images=image, return_tensors="pt").to(model.device)
outputs = model.generate(**inputs, max_new_tokens=4096, temperature=0.1)
print(processor.decode(outputs[0], skip_special_tokens=True))

Vision Prompt

The model was trained with this bilingual prompt (use it at inference for best results):

You are a construction safety vision system. Analyze the provided image of a construction site and identify ALL safety hazards.

For each hazard detected, provide:
1. type: Category — one of: fall_hazard, electrical_hazard, ppe_violation, equipment_hazard, public_safety, structural_hazard, cable_hazard, environmental_hazard
2. description: Bilingual description — English first, then Japanese in parentheses
3. confidence: 0.0–1.0
4. location: Bounding box as {x, y, width, height} in percentage of image (0–100)
5. severity: low / medium / high / critical

Also provide:
- site_type: "high_rise" | "road_construction" | "renovation" | "other"
- site_description: Bilingual description of the construction site
- environmental_conditions: weather, lighting, ground_condition

Return ONLY valid JSON.

Output Format

{
  "site_type": "high_rise",
  "site_description": "Multi-story building under construction with exposed steel framework (鉄骨フレームが露出した多層建築工事現場)",
  "hazards": [
    {
      "id": "H1",
      "type": "ppe_violation",
      "description": "Worker without hard hat near scaffolding (足場付近でヘルメット未着用の作業員)",
      "confidence": 0.92,
      "severity": "critical",
      "location": { "x": 35.2, "y": 42.1, "width": 8.5, "height": 15.3 }
    }
  ],
  "environmental_conditions": {
    "weather": "clear",
    "lighting": "daylight",
    "ground_condition": "dry"
  }
}

Training Details

Method

Teacher Distillation with LoRA — Qwen3.5-27B (served via vLLM) annotated ~950 construction site images with structured hazard JSON. The annotations were used to fine-tune Pixtral 12B via LoRA using MS-Swift + DeepSpeed ZeRO-2.

Dataset

Image sources:

• keremberke/construction-safety-object-detection (~398 images)
• Francesco/construction-safety-gsnvb (600 images)
• Internal reference images (37 images)

Hyperparameters

Hardware

• 4x NVIDIA H200 (141 GB) for training
• 2x NVIDIA H200 for inference (vLLM, tensor parallel)

Hazard Categories

Evaluation

Evaluated using W&B Weave with 4 custom scorers:

• JsonValidityScorer — JSON format compliance
• HazardF1Scorer — Hazard type detection F1
• SeverityAccuracyScorer — Severity classification accuracy
• BBoxIoUScorer — Bounding box IoU

The primary improvement is in violation recall (+48.8 pp), which is the most safety-critical metric — missing a PPE violation in a real construction site can lead to injuries or fatalities.

Limitations

• Trained primarily on outdoor construction sites; indoor renovation scenes may have lower accuracy
• Bounding boxes are approximate (trained from VLM teacher, not manual annotation)
• Environmental condition detection (weather, lighting) is based on visual cues only
• Model inherits biases from the Pixtral 12B base and Qwen3.5-27B teacher

Citation

@misc{evoboard2026,
  title={Mistral EvoBoard: AI Safety Committee for Construction},
  author={Takashi Shibata},
  year={2026},
  url={https://github.com/TakashiShibata/Mistral-Hackathon-2026}
}