Email to professional for clarifying some rules as stipulated in the formal letter

I would like to write an email to professional for clarifying some rules as stipulated in the formal letter. Please help to correct my sentences below. Thanks

Dear Sir / Madam

According to a letter no. 123 regarding the case 88 (Primary Air Handling Unit (PAU) with ducted fresh air supply for Air Handling Unit (AHU)s with ducted return serving multi-compartment multi-floor), I have problems about the letter shown in the below.

Using the case 88 as an example: Four nos. of AHU and one PAU with all air flow rate over 1000 l/s are assumed to be installed in a building. PAU is located at roof floor and four AHUs are installed on different floors. PAU provides fresh air via ductwork connected with and distributed to all AHUs.

1. I don't understand the statement shown in the letter that PAU can only be operated when any one of the AHU is running.

It means that only one AHU is tripped by a probe type smoke detector. The PAU can be operated normally due to other three AHU are still running in the building. Am I correct?

1. I don't understand the statement shown in the letter that the probe type smoke detector installed at any AHU will activate the tripping function of PAU and AHU of respective floor.

According to the statement, the PAU is tripped by one AHU if only one floor has fire and smoke. It means three AHUs are operating normally. Smoke will spread to other floors via fresh air duct due to the creation of negative pressure in the fresh air ductwork system when the other three AHU is running normally. Is it correct?

1. Is it required all the AHU and PAU to be tripped simultaneously when any probe type smoke detector detecting the smoke at any one floor to ensure the safety of human life as the first priority at any situation?

1. Is it required to resume the PAU operation when any one of the AHU is running after confirming all venues in safe condition?