I limit my answer to U.S. law.
The Right To Quit And Its Impact On Unemployment Benefits
First, absent narrow exceptions (e.g. soldiers), any employee can quit at any time, from work with a bad employer.
Normally quitting forfeits a right to unemployment insurance payments, but if the employee can convince the unemployment eligibility hearing office that the conditions the employer established were so bad that there was a "constructive discharge" the employee will be treated as having been fired for purposes of unemployment insurance.
The employee can't get an advisory opinion on constructive discharge, however. The employee must act first and argue that there was a constructive discharge afterwards at risk of not getting any unemployment benefits if the employee loses.
Occupational Safety and Health Laws
Second, the employer is obligated to follow workplace safety law. Outside the mining industry (which does not include oil and gas work), workplace safety regulations are primarily promulgated by OSHA (the Occupational Safety and Health Administration) which is a subdivision of the federal department of Labor. Many states have a parallel state agency. (The mining industry is governed by MHSA a parallel and much more powerful body.)
Violating workplace safety rules established by OSHA can result in the employer being fined and being required to correct the situation going forward, although the amounts of the fine even taken together with worker's compensation packages, are often far less than the amount of liability that the employer would have in a third-party negligence lawsuit. The government and not the employee receives the fine paid if one is imposed.
Also, OSHA is vastly understaffed and routinely ignores worker complaints out of sheer lack of manpower, since it is responsible for all safety issues for 98%+ of all employees in the entire United States.
OSHA has protocols related to requirements for employees working in extreme heat that are discussed here. In particular, OSHA states that:
Washington, Minnesota, and California have specific laws governing
occupational heat exposure. Federal OSHA has a General Duty Clause
(Section 5a of the Occupational Safety and Health Act of 1970)
that requires employers to provide a place of employment that is “free
from recognized hazards that are causing or are likely to cause death
or serious physical harm to employees.” The OSHA Technical Manual
Chapter on Heat Stress establishes that OSHA uses WBGT to determine if
a heat hazard was present.
Thus, outside those three states, rather than having detailed requirements in a regulation, OSHA has general suggestions and provides a framework for evaluating heat related safety and occupational illness issues that gets evaluated on a case by case basis if OSHA asserts that an employer has violated these general safety requirements, which will be resolved in a hearing, if necessary, if a citation issued by OSHA on this basis is issued by OSHA and disputed by the employer.
Third, the employer has liability without regard to fault for all work related injuries, illness and deaths under worker's compensation law. The employer has liability even if the employer didn't violate any OSHA regulations or standards.
But, the recovery allowed is much more meager than it would be between strangers suing each other for negligence. It is largely limited to lost wages, medical expenses, and funeral expenses, although if a deceased worker has dependents, their dependent survivors are also entitled to worker's compensation lost income benefits.
The existence of worker's compensation coverage, however, bars an employee from bringing a lawsuit other than a worker's compensation claim against the employer, however.
Collective Bargaining Rights Of Unionized Workers
Fourth, in a unionized workplace, the union could raise a grievance with the employer under the collective bargaining agreement governing the workplace which will universally require the employer to follow safety rules.
If there is a dispute, these disputes are typically referred to an arbitrator in union-management arbitration. The arbitrator has considerable freedom to fashion remedies if the arbitrator feels that the safety rules were not followed. Neither side can appeal the arbitrator's ruling.
If the employer does not follow an order from an arbitrator, this is converted to a court order at an ordinary court with jurisdiction over the employer and the court will make the arbitrator's order a court order which may be enforced under pain of contempt of court sanctions (including incarceration or punitive fines).