Hello!
Because it is a Firewall board, I will answer only the Firewall relationship.
First of all, FMC4600, DN2-HW-APL-L, SNS-375 are UCS-based, "When the CPU temperature becomes 82 degrees or more (for protection), the CPU will stop", so I think that this area is actually not a threshold.
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Excerpt:
The Cisco UCS equipment should operate in an environment that provides an inlet air temperature not colder than 50°F (10°C) nor hotter than 95°F (35°C). If sensors on a CPU reach 179.6°F (82°C), the system will take that CPU offline.
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/hw/site-prep-guide/ucs_site_prep/ucs_siteprep_chapter_010.html#:~:text=The%20Cisco%20UCS%20equipment%20should,will%20take%20that%20CPU%20offline.
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It seems that the FPR4100 is also at the upper limit of 82 degrees.
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Excerpt:
fltMemoryUnitThermalThresholdNonCritical
The Cisco FPR device should operate in an environment where the expiratory temperature is not below 10°C (50°F) and 35°C (95°F).
When the CPU sensor reaches 82°C (179.6°F), the system takes the CPU offline.
https://www.cisco.com/c/ja_jp/td/docs/security/firepower/fxos/fxos281/faults/FXOSFaultsErrorsRef/FXOS_SEMs.html
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I couldn't find any information about FPR3100, but FPR1000/2100 seems to have an upper limit of 82 degrees, so I think FPR3100 is likely the same.
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https://www.cisco.com/c/ja_jp/td/docs/security/firepower/2100/faults/660/FXOSFaultsErrorsRef/FXOS_SEMs.html#pgfId-2157256
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If there is no such description in the manual of the product you are planning to use, it may be a non-public specification, and if you want to know for any reason, I think it is useful to ask the manufacturer (Cisco) based on the contract information of each product.
