Date: 202112
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Takeoff / Launch
Airspace: Class C ZZZ
ATC / advisory: Ramp ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Distraction; Communication Breakdown
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Ground Personnel
When detected: Aircraft In Service At Gate; Routine Inspection
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Event occurred during preflight/ground operations in ZZZ after checking the ADG (Accessible Dangerous Goods) container and receiving the Captains signature on the aircraft DG manifest. As I returned a signed copy of the aircraft DG manifest to the Ramp Agent I also handed them the red/white striped DG paper-work folder. Neither myself or the Ramp Agent recognized this and we departed ZZZ for ZZZ1 without the folder on board aircraft. I still retained a signed copy of the aircraft DG manifest in my pocket; but did not have the red/white folder. The event was recognized in ZZZ1 when the Ramp Agent could not find the red/white folder. It was an oversight and mistake on my part.Overall; It was a momentary brain lapse that caused this. One Contributing factor was rapidly changing weather conditions (snow/visibility) captured my attention/thoughts. While starting/thinking ahead is important; this could have been prevented by simply slowing down and handling one task at a time.


Second narrative: As a B757 crew we potentially performed a take-off below take-off minimums on Runway XXR at ZZZ. At show time the weather was 10SM vis/CLR skies. However; about 10 minutes prior to pushback a snow storm moved into the area and the weather began rapidly changing. We decided to de-ice/anti-ice. This; along with getting stuck behind addition de-icing aircraft on the ramp; led to delays leaving ZZZ. As we finally taxied we continued to monitor for new ATIS information. As we waited to depart behind an aircraft in front of us; the visibility dropped to 1/2 SM. It was originally my take-off as the FO (First Officer); however my Captain made the decision to perform the takeoff himself due to the snowy conditions and changing visibility. While waiting on the taxiway; behind an aircraft in front of us; my Captain checked the page for takeoff minimums on Runway XXR at ZZZ. He saw that 1/2 SM was the Standard Takeoff mins for that runway. However; after reviewing it later it was determined that he misread the chart as 1/2 SM was the STD mins for 3 or more engine aircraft and 1 SM for 2 engine aircraft (we were operating a B757). I did not look up the page for myself and therefore did not do a good job at backing up the Captain on the decision to depart. However; we departed ZZZ on XXR without incident. Later; After discussing what occurred; we recognized that taking off with 'Adequate Visual Reference' required 1/4 SM vis. We could both definitely agree that we had more than adequate visual references to take-off as the HIRL and runway marking were easily visible throughout the takeoff procedure. However; neither of us was 100% sure that those mins (1/4 SM) applied to us in that situation. We are continuing to do research and reach out to knowledgeable resources.


Synopsis: Air Carrier flight crew reported gate departure without required Hazmat document folder. Flight crew did have a signed copy of the DG manifest but not the required company folder.