्सुरक्षा ही पहली बात

I think it is appropriate for slogan.

Since this has to serve as a slogan, this can be another choice which means that safety is the foremost.

--------------------------------------------------
Note added at 1 hr (2006-01-21 01:04:36 GMT)
--------------------------------------------------

सुरक्षा सर्वोपरि

--------------------------------------------------
Note added at 3 hrs (2006-01-21 02:48:04 GMT)
--------------------------------------------------

You may also consider:

Suraksha hii sarvopri hai---सुरक्षा ही सर्वोपरि है---(Safety is foremost)

Pehlii prAthmiktA - SurakshA--पहली प्राथमिकता - सुरक्षा---(The First Priority - Safety)

This is not the literal translation but quite capable of conveying the sense.

No explanation needed

Yes, Hindi is the most prevalent language in India. It is spoken by roughly half the population of India, or about 500 million people. It is also widely understood in all the major cities in the non-Hindi speaking areas of the country like Calcutta, Mumbai, Hyderabad, Bangalore and Chennai. Also, the younger generation (school-attending) would all be familiar with Hindi as they learn it at school for about 10 years as a second language. Hindi is also the official language of India.

So your choice about Hindi as a representative language of India is without fault.

Coming to your other question, one possibility is:

सुरक्षा सर्वप्रथम (Suraksha Sarvapratham).

This means exactly Safety First. There is also the alliteration in the repetition of the S sound which makes the slogan more catchy and memorable.

Saftety is to be given maximum importance